Pathology Review Ch 27
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A 5-year-old boy develops increasing muscle weakness. He is unable to play with other children because he quickly becomes tired and is unable to keep up with them. On physical examination, he is afebrile. No deformities are noted. He has 4/5 muscle strength in his extremities, with more apparent weakness of the proximal muscles. Laboratory studies show a serum creatine kinase level of 689 U/L. A muscle biopsy is done; the figure shows the appearance of the biopsy specimen at low magnification. Which of the following tests would be most appropriate to determine the diagnosis in this boy?
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Serum acetylcholinesterase antibody titer
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Immunohistochemical staining for dystrophin
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Eosinophil count in blood
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Presence of oligoclonal bands of immunoglobulin in cerebrospinal
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PCR to detect expansion of CGG repeats on Xq27.3
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.JPG "A 5-year-old boy develops increasing muscle weakness. He is unable to play with other children because he quickly
becomes tired and is unable to keep up with them. On physical examination, he is afebrile. No deformities are noted. He
has 4/5 muscle strength in his extremities, with more apparent weakness of the proximal muscles. Laboratory studies show
a serum creatine kinase level of 689 U/L. A muscle biopsy is done; the figure shows the appearance of the biopsy
specimen at low magnification. Which of the following tests would be most appropriate to determine the diagnosis in this
boy?")
About This Quiz
This Pathology Review CH 27 quiz assesses knowledge on various musculoskeletal disorders through clinical scenarios. Topics include muscle weakness, sensory changes, and acute and chronic diseases affecting muscle function. It targets key diagnostic skills relevant for medical students and professionals.
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- 2.
A 25-year-old woman has had episodes of numbness and tingling in both hands for 5 months. The problem typically occurs near the end of the day and makes it difficult for her to use the computer keyboard. The thumb and first two fingers are most affected. There is no pain or swelling, and she does not recall any trauma to the upper extremities. On physical examination, she has decreased sensation to light touch and pinprick over the palmar surface of both hands in the distribution of the first three digits. Thenar muscle atrophy seems to be present. Which of the following conditions is most likely causing her problem?
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Repetitive stress injury
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Diabetes mellitus
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Amyotrophic lateral sclerosis
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Acute intermittent porphyria
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Varicella-zoster virus infection
Correct Answer
A. Repetitive stress injuryExplanation
(A) This patient has carpal tunnel syndrome, a form of compression neuropathy, which results from entrapment of the
median nerve beneath the flexor retinaculum at the wrist. Women are more commonly affected than men, and the problem
is often bilateral. The most common cause is excessive repetitive use of the wrist. Conditions such as hypothyroidism,
amyloidosis, and edema with pregnancy also diminish the space in the carpal tunnel. Diabetes mellitus leads to a
symmetric distal sensorimotor neuropathy. Amyotrophic lateral sclerosis results in progressive symmetric weakness from
loss of motor neurons. Acute intermittent porphyria can lead to a hereditary form of motor and sensory neuropathy.
Infection with varicella-zoster virus produces a painful neuropathy in a dermatomal distribution pattern.
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- 3.
A 63-year-old man has been receiving hemodialysis for chronic renal failure and has noted increasing loss of sensation in his legs for the past 4 years. On physical examination, there is symmetrically decreased sensation over both lower extremities. He has no decrease in strength or abnormality of gait. What is most likely to produce these findings?
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Guillain-Barré syndrome
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Cerebral astrocytoma
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Cerebral infarction
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Diabetes mellitus
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Multiple sclerosis
Correct Answer
A. Diabetes mellitusExplanation
(D) The most common cause of a predominantly sensory peripheral neuropathy is diabetes mellitus. Long-standing
diabetes mellitus also gives rise to renal failure. Guillain-Barré syndrome produces a rapidly ascending paralysis.
Sensorimotor disturbances are typically not seen with intracranial mass lesions such as astrocytomas. A cerebral infarction
could lead to decreased motor activity and sometimes to sensory loss, although not in a symmetric pattern. The
demyelinating lesions of multiple sclerosis can produce many signs and symptoms, but symmetric lesions should suggest
another disease process.
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- 4.
A 17-year-old boy has had generalized muscle pain with fever for 1 week. Over the past 2 days, he has developed increasing muscular weakness and diarrhea. On physical examination, his temperature is 38°C. All of his muscles are tender to palpation, but he has a normal range of motion, and no significant decrease in muscle strength. Laboratory findings include hemoglobin, 14.6 g/dL; hematocrit, 44.3%; MCV, 90 μm3; platelet count, 275,000/mm3; and WBC count, 16,700/mm3 with differential of 68% segmented neutrophils, 6% bands, 10% lymphocytes, 4% monocytes, and 12% eosinophils. What is the most likely diagnosis?
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Duchenne muscular dystrophy
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Polymyositis
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Poliomyelitis
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Trichinosis
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Diabetes mellitus
Correct Answer
A. TrichinosisExplanation
(D) Muscle pain with fever and eosinophilia suggests a parasitic infestation of the skeletal muscles, most likely
trichinosis; this results from ingesting poorly cooked infected meat. Duchenne muscular dystrophy is a noninflammatory
myopathy that begins in early childhood. Polymyositis is an autoimmune condition characterized by muscle inflammation,
but no eosinophilia. Poliomyelitis can lead to muscle weakness, but is noninflammatory. Diabetes mellitus can lead to
peripheral vascular disease and gangrene, but this complication would be rare at age 17.
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- 5.
An infant born at term exhibits difficulty with movement beginning at 1 month of age. By 1 year of age, there is flaccid paralysis. A muscle biopsy is done, and microscopically shows panfascicular atrophy of myofibers with scattered enlarged myofibers, but no inflammation. The serum creatine kinase is not elevated. What is the most likely diagnosis?
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Amyotrophic lateral sclerosis
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Duchenne muscular dystrophy
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McArdle disease
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Myasthenia gravis
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Myotonic dystrophy
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Werdnig-Hoffmann disease
Correct Answer
A. Werdnig-Hoffmann diseaseExplanation
(F) This infant has Werdnig-Hoffman disease, a form of spinal muscular atrophy resulting from loss of motor neurons in
infancy, so the biopsy specimen shows group atrophy of myofibers. Death is inevitable by age 3 years. Amyotrophic lateral
sclerosis is a progressive disease with a neurogenic form of muscle atrophy resulting from loss of motor neurons.
Duchenne muscular dystrophy has an X-linked pattern of inheritance and onset in childhood, and there is a mutation in the
dystrophin gene. McArdle disease is an autosomal recessive condition resulting from a deficiency in muscle
phosphorylase and does not produce progressive weakness. Myasthenia gravis results from acetylcholine receptor
antibody and leads to progressive weakness. Myotonic dystrophy is characterized by facial and upper body weakness,
cataracts, gonadal atrophy, cardiomyopathy, and dementia.
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- 6.
A 40-year-old man had an influenza-like illness for 1 week. A few days later, he experienced a rapidly progressive, ascending motor weakness that required intubation and mechanical ventilation. On physical examination, he is now afebrile and has 3/5 motor strength in his extremities. A lumbar puncture is done and yields clear, colorless cerebrospinal fluid under normal pressure. The cerebrospinal fluid has a slightly elevated protein concentration, but a normal glucose level, and a cell count with only a few mononuclear cells. The patient recovers in 3 weeks. If lymphocytic infiltrates were seen in peripheral nerves along with segmental demyelination at the time he initially saw his physician, what would be the most likely diagnosis?
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Guillain-Barré syndrome
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Multiple sclerosis
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Amyotrophic lateral sclerosis
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Varicella-zoster virus infection
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Vitamin B12 (cobalamin) deficiency
Correct Answer
A. Guillain-Barré syndromeExplanation
(A) The patient's history is typical of Guillain-Barré syndrome. This uncommon disorder most often follows a viral or
mycoplasmal infection. It is believed to be caused by generation of myelin-reactive T cells, somehow triggered by viral
infection. The paralysis of respiratory muscles may be life-threatening, although many patients recover after weeks of
ventilatory support. Various presentations are possible in multiple sclerosis, but the plaques of demyelination are generally
not large or diffuse enough to cause paralysis of the respiratory muscles. Amyotrophic lateral sclerosis is associated with
slowly progressive muscle weakness. Mechanical ventilation may be necessary eventually. Varicella-zoster virus infection
most often involves the skin in a dermatomal distribution from a spinal nerve root. Vitamin B12 deficiency results in subacute progressive degeneration of the spinal cord plus sensorimotor disturbances in the extremities.
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- 7.
For the past month, a 56-year-old man has experienced worsening double vision and eyelid drooping, particularly toward the end of the day. He also has had difficulty chewing his food at dinner. He was diagnosed with Sjögren syndrome more than a decade ago. On physical examination, he has 5/5 motor strength in his extremities that decreases to 4/5 strength with repetitive movement. There is no pain on palpation and no decrease in joint mobility. Which of the following laboratory findings is most likely to be reported for this patient?
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Elevated serum creatine kinase level
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Acetylcholine receptor antibody positivity
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Peripheral blood eosinophilia
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Increased serum cortisol level
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Antihistidyl tRNA synthetase (anti-Jo-1) titer 1 : 512
Correct Answer
A. Acetylcholine receptor antibody positivityExplanation
(B) This patient has myasthenia gravis, with muscle weakness resulting from loss of motor end plate function. This
disorder is caused by an antibody-mediated loss of acetylcholine receptors at neuromuscular junctions. Myopathic
diseases such as muscular dystrophies are accompanied by increased levels of serum creatine kinase. Parasitic infection
with Trichinella spiralis can lead to eosinophilia. Generalized muscle weakness with type II muscle fiber atrophy occurs in
glucocorticoid excess. The anti-Jo-1 antibody is present in polymyositis. Sjögren syndrome does not cause muscle
weakness with use.
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- 8.
A 72-year-old man has had a 7-kg weight loss, proximal muscle weakness, and difficulty with urination for the past 4 months. On physical examination, he has 4/5 muscle strength in his extremities with repetitive motion. He has no muscle pain or loss of mobility. Laboratory studies show that he does not have serum antibodies to acetylcholine receptor. He was prescribed anticholinesterase agents but shows no improvement. Which of the following underlying conditions is most likely to be present?
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Chronic hepatitis C
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Duchenne muscular dystrophy
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Small-cell lung carcinoma
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Lead poisoning
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Diabetes mellitus
Correct Answer
A. Small-cell lung carcinomaExplanation
(C) This patient has a paraneoplastic syndrome called Lambert-Eaton myasthenic syndrome. Similar to many
paraneoplastic syndromes, it is most often associated with small-cell carcinoma of the lung. Patients with chronic viral
hepatitis may have generalized malaise and weakness that is not related to specific muscle disease. Duchenne muscular
dystrophy is an X-linked disease that manifests early in childhood. Lead poisoning leads to peripheral neuropathy.
Diabetes mellitus also may produce peripheral neuropathy.
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- 9.
A 56-year-old woman has had increasing generalized muscle weakness for the past 2 months. On physical examination, she has 3/5 motor strength in upper and lower extremities. She has fat redistribution in the upper trunk and rounded facies. Ecchymoses are scattered over the extremities. She is afebrile, and her blood pressure is 155/90 mm Hg. A biopsy specimen of the gastrocnemius muscle is obtained, and histochemical staining shows type II muscle fiber atrophy. What is the most likely diagnosis?
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Cushing syndrome
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McArdle disease
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Duchenne muscular dystrophy
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Myasthenia gravis
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Polymyositis
Correct Answer
A. Cushing syndromeExplanation
(A) Type II atrophy can occur with glucocorticoid excess and after prolonged immobilization. Routine light microscopy
may not allow the physician to distinguish type II atrophy from denervation atrophy. Histochemical staining for ATPase
must be done. There is a deficiency of myophosphorylase enzyme in McArdle disease, leading to muscle pain and
cramping with vigorous exercise. Duchenne muscular dystrophy is an X-linked condition and is rare in females. Onset is in
early childhood. Antibodies to the acetylcholine receptor cause the muscular weakness in myasthenia gravis. Polymyositis
is an inflammatory condition affecting all fiber types.
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- 10.
A 44-year-old man has had worsening exercise intolerance for the past year. On physical examination, he has 4/5 motor strength in the extremities, but has no muscle pain or loss of joint mobility. He has pitting edema to the knees. A chest radiograph shows cardiomegaly with pulmonary edema and pleural effusions. A deltoid muscle biopsy specimen is obtained. The figure shows the immunohistochemical staining pattern with antibody to dystrophin (A, normal; B, patient). What is the most likely diagnosis?
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Werdnig-Hoffmann disease
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Polymyositis
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Becker muscular dystrophy
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Amyotrophic lateral sclerosis
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Myasthenia gravis
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Myotonic dystrophy
Correct Answer
A. Becker muscular dystrophyExplanation
(C) The biopsy specimen shows reduced amounts of dystrophin, suggesting Becker muscular dystrophy. In Duchenne
muscular dystrophy, dystrophin is absent because of gene deletion. In keeping with the diagnosis of Becker muscular
dystrophy, the patient is older and not severely affected. Both dystrophies are X-linked conditions. Werdnig-Hoffmann
disease is a form of spinal muscular atrophy. Onset is at birth, and it results from a genetically determined loss of anterior
horn cells. Polymyositis is an autoimmune disease that results from a T cell–mediated attack on muscle fibers, causing
muscle fiber degeneration with inflammation. Amyotrophic lateral sclerosis is a denervation atrophy seen in adults, with
loss of anterior horn cells in the spinal cord and cranial nerve nuclei. Myasthenia gravis results from acetylcholine-receptor
antibody, and there is minimal structural change to the muscle. Myotonic dystrophy is characterized by facial and upper
body weakness, cataracts, gonadal atrophy, cardiomyopathy, and dementia.
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- 11.
A 40-year-old man undergoes elective laparoscopic hernia repair. He receives anesthesia with halothane and succinylcholine. His blood loss is minimal. Thirty minutes into this surgery, his temperature increases to 39.5°C, and pulse increases to 115/min. The anesthesiologist notices muscular spasms with rigidity of the extremities. Laboratory studies show an elevated serum creatine kinase and myoglobinuria. This man most likely has an inherited disorder with a gene encoding for a protein involved with which of the following?
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Calcium ion channel
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Motor end plate
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Oxidative phosphorylation enzyme
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Sarcoglycan complex
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Thick filament
Correct Answer
A. Calcium ion channelExplanation
(A) This patient has malignant hyperthermia, a rare but life-threatening disorder seen in only 1 in 20,000 adults, but
with millions of surgical procedures under anesthesia being performed, it must be considered when the patient's
temperature increases rapidly. There is impaired reuptake of calcium into the sarcoplasmic reticulum with increased
intracellular calcium leading to hypermetabolism. Motor end plates include acetylcholine and acetylcholine receptors that
are involved with myasthenia gravis. The mitochondrial DNA genes are mainly involved in oxidative phosphorylation, and
there is a maternal inheritance pattern, with possible muscular weakness, but not hyperthermia. The sarcoglycan complex
includes many proteins such as dystrophin that can be involved with muscular dystrophies, but not hyperthermia. Thick
filaments include the myosin contractile protein; β-myosin mutations are found in some cases of hypertrophic
cardiomyopathy.
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- 12.
A 93-year-old woman has been bothered by continuing outbreaks of painful lesions on the skin of her right chest for the past year. On physical examination, there is a vesicular eruption over a 1 × 8 cm area over the right seventh rib. She is treated with acyclovir, and resolution of the skin lesions occurs, but the pain persists for the next 3 months. Which of the following is the most likely cause for her findings?
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Aging
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Diabetes mellitus
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Multiple sclerosis
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Somatoform pain disorder
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Vitamin B12 (cobalamin) deficiency
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Varicella-zoster virus infection
Correct Answer
A. Varicella-zoster virus infectionExplanation
(F) After infection with chickenpox the varicella-zoster virus (VZV) becomes dormant in dorsal root ganglia, only to
reactivate later when the immune system no longer contains it. Such containment failures are more likely with age and with
immunocompromised states, and this produces the classic appearances of shingles in a dermatomal distribution. She also
has postherpetic neuralgia, a disabling condition of chronic pain that is difficult to manage. Aging alone does not explain
disease, but older individuals are more likely to have disease conditions. Diabetes mellitus leads to neuropathies that can
have loss of sensation or even pain, but there are no associated skin lesions. Multiple sclerosis can involve the spinal cord
white matter with variable neurologic findings, but there are no skin lesions, and the onset of MS is at a younger age. Pain out of proportion to the pathologic findings suggests a somatoform pain disorder, but she does have significant pathologic
findings that explain her continued pain. Pernicious anemia with subacute combined degeneration of the spinal cord can
lead to paresthesias and loss of function, but not to skin lesions.
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- 13.
A 55-year-old man visits the physician because he has had a foot ulcer for 2 months that has not healed. Physical examination shows a 2-cm shallow, nonhealing ulceration of the left medial malleolus. There is symmetric decreased sensation in the distal regions of the lower extremities. The patient has a history of multiple urinary tract infections resulting from difficulty in completely emptying the bladder. He is impotent. Which of the following pathologic findings is most likely to be present in the peripheral nerves?
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Wallerian degeneration
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Acute inflammation
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Onion bulb formation
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Endoneurial lymphocytic infiltration
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Axonal neuropathy
Correct Answer
A. Axonal neuropathyExplanation
(E) The features described are consistent with a peripheral neuropathy associated with diabetes mellitus. Motor and
sensory nerves are involved, and there may be an autonomic neuropathy. Histologic examination shows an axonal
neuropathy with segmental demyelination. Difficulty in emptying the urinary bladder and impotence are results of
autonomic neuropathy. Longer nerves are affected first; this explains the lower leg involvement and accounts for many
cases of diabetic foot, with trauma and subsequent ulceration. Wallerian degeneration typically occurs with traumatic
transection of a nerve. Acute inflammation is not generally seen in neuropathies. Onion bulb formation is a feature of the
hereditary neuropathy known as Refsum disease. Lymphocytic infiltrates may be seen in Guillain-Barré syndrome.
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- 14.
A 42-year-old man has had increasing progressive muscle weakness in both arms and legs and dysarthria and difficulty in swallowing for the past 2 years. He is now wheelchair-bound. Physical examination shows 3/5 motor strength in all extremities. He has no muscle pain on palpation, no deformities or loss of joint mobility, and no tremor. A biopsy specimen of the quadriceps muscle is obtained, and microscopic examination shows a pattern of grouped atrophy of the myofibers. What is the most likely diagnosis?
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Werdnig-Hoffmann disease
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Amyotrophic lateral sclerosis
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Becker-type muscular dystrophy
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Myasthenia gravis
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Mitochondrial myopathy
Correct Answer
A. Amyotrophic lateral sclerosisExplanation
(B) Amyotrophic lateral sclerosis is also known as Lou Gehrig disease, named for the famous New York Yankee first
baseman affected with the disorder. Lower and upper motor neurons can be affected, resulting in a denervation-type
pattern of muscular atrophy. This occurs because an individual neuron innervates a group of muscle fibers. Bulbar
involvement denotes a more rapid course. Werdnig-Hoffman disease also is a neuropathic disease with grouped atrophy,
but onset is in infancy. The other listed options are not associated with denervation.
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- 15.
A 16-year-old boy has a deep laceration of the upper left anterior thigh. The bleeding is stopped. On physical examination, he has loss of sensation in and movement of the left foot. The wound is surgically repaired, and he receives physical therapy. How long will it take him to regain the use of his left foot?
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1 day
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1 week
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1 month
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1 year
Correct Answer
A. 1 yearExplanation
(D) Laceration of the femoral nerve results in wallerian degeneration distal to the injury. Realignment of the nerve is
accompanied by axonal sprouting. The new axons find the residual myelin sheaths and grow down at the rate of about 2
mm/day, taking 1 year for the distance of a lower extremity. There can be reinnervation of the muscle, but there is type
grouping of the muscle fascicles that are reinnervated.
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- 16.
A 41-year-old woman has noted marked pain in the right foot for the past 2 months. The pain makes it difficult for her to wear high-heeled shoes and seems to be worse at the end of the day. On physical examination, she has severe pain on palpation of the interdigital space between the second and third toes. There is no swelling or erythema of the foot. Motor strength in the lower extremities seems to be normal. What has most likely produced these findings?
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Diabetes mellitus type 1
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Diabetes mellitus type 2
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Entrapment neuropathy
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Lead poisoning
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Thiamine deficiency
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Vitamin B12 (cobalamin) deficiency
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Wallerian degeneration
Correct Answer
A. Entrapment neuropathyExplanation
(C) Fashion may have a price. The patient has a Morton neuroma, a form of compressive neuropathy in which a
plantar nerve is trapped between metatarsal heads. Chronic injury leads to growth of a tangled mass of axons, fibroblasts,
and perineural cells. The toxic disorder (lead poisoning) and metabolic disorders (beriberi with thiamine deficiency or
subacute combined degeneration with cobalamin deficiency) are not as focal. Diabetic neuropathy, which occurs in either
type 1 or type 2 disease, is bilateral. It is characterized by loss of sensation, which may be a predisposing factor for foot
trauma. Wallerian degeneration is a dying-back neuropathy associated with severing of a nerve; a neuroma may form at
the site of injury.
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- 17.
A 16-year-old boy has had two episodes of sudden loss of motor function with residual weakness in his right arm and right leg in the past 2 years. He has had muscle weakness and a seizure disorder since childhood. During the past year, he has had difficulty with memory and performing activities of daily living. On physical examination, he has short stature. He has 4/5 motor strength in all extremities, with no muscle tenderness. Laboratory studies show Na+, 141 mmol/L; K+, 4.1 mmol/L; Cl−, 95 mmol/L; CO2, 19 mmol/L; glucose, 71 mg/dL; creatinine, 1.1 mg/dL; and lactic acid, 9.2 mmol/L. A gastrocnemius muscle biopsy specimen is obtained, and microscopic examination shows ragged red fibers. On electron microscopy, the myofibrils have “parking lot” inclusions. The boy's mother and grandmother had similar findings, but his father and grandfather did not. Which of the following most likely explains the pathogenesis of his disease?
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Abnormal voltage-gated calcium channel
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Antibodies to acetylcholine receptor
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Cytotoxic CD8+ lymphocytes
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Decreased sarcolemmal dystrophin
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Deficient mitochondrial enzyme
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Increased CTG repeat sequences at 19q13.2–13.3
Correct Answer
A. Deficient mitochondrial enzymeExplanation
(E) Oxidative phosphorylation in mitochondria can be affected by mitochondrial genes, which are separate from those
on chromosomes in the cell nucleus. These abnormal genes can lead to mitochondrial myopathies, encephalopathies, and
deafness. In this case, there is mitochondrial encephalopathy with lactic acidosis and strokelike episodes (MELAS).
Mitochondrial genes have a maternal pattern of inheritance. An abnormal voltage-gated calcium channel is seen in one of
the channelopathies; it causes hypokalemic periodic paralysis. Channelopathies are typically inherited in an autosomal
dominant fashion. Antibodies to acetylcholine receptor cause myasthenia gravis; its sole manifestation is muscle
weakness. Cytotoxic CD8+ cells mediate the muscle injury in polymyositis. Decreased sarcolemmal dystrophin is present
in Becker muscular dystrophy; dystrophin is absent in Duchenne muscular dystrophy. The dystrophin gene is located on
the X chromosome. Increased CTG repeats occur in myotonic dystrophy.
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- 18.
A 62-year-old woman has a slowly enlarging mass anterior to the right ear. Surgery is performed to remove a pleomorphic adenoma of the parotid gland. The tumor has infiltrated the overlying soft tissue, and the surgeon must remove a portion of the facial nerve to obtain an adequate margin. He places a 2-cm nerve graft in the excised area. Which of the following best describes the most likely outcome during the first week after surgery?
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Appearance of acute inflammation around the graft
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Formation of a traumatic neuroma
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Grouped atrophy of facial muscles
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Growth of recurrent tumor along the nerve graft
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Wallerian degeneration in the distal facial nerve
Correct Answer
A. Wallerian degeneration in the distal facial nerveExplanation
(E) The axons distal to the point of injury or transection degenerate. The Schwann cells that remain can guide the
regrowing nerves. Macrophages help to remove myelin-derived debris from the area of nerve injury, but acute
inflammation is not a typical feature of diseases involving peripheral nerves. Traumatic neuromas may occur after
transection. The purpose of the graft is to guide orderly regrowth. A tumor is unlikely to follow a nerve, although a feature
of a malignant tumor is a tendency to invade nerves. Grouped atrophy occurs later with progression of disease when
denervation is followed by reinnervation.
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- 19.
A 30-year-old woman has had gradually increasing muscle weakness with myalgia for the past year. She now has difficulty getting up from a chair and climbing stairs. She does not have weakness of her hand muscles, however. Physical examination reveals a fine violaceous rash on her face, predominantly palpebral. Dusky flat red patches are present on her elbows, knees, and over her knuckles. Laboratory serum studies show creatine kinase of 620 U/L. Electromyography shows increased spontaneous activity with fibrillations, complex repetitive discharges, and positive sharp waves. A deltoid biopsy specimen is obtained, and on microscopic examination shows a mononuclear inflammatory cell infiltrate around small blood vessels and groups of atrophic myofibers at the periphery of fascicles. What mechanism is most likely responsible for her disease?
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Myofiber injury by CD8+ T cells directed against muscle antigens
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T cell–mediated peripheral nerve injury induced by Mycoplasma pneumoniae infection
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Antibody- and complement-mediated injury to the microvasculature
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Mutation in a gene encoding for voltage-gated calcium channels
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Expansion of CTG repeat sequences on chromosome 19q13.2
Correct Answer
A. Antibody- and complement-mediated injury to the microvasculatureExplanation
(C) The clinical features and histologic findings are typical of dermatomyositis, an immunologically mediated form of
inflammatory myopathy. In these patients, antibodies and complement damage small capillaries, resulting in a
characteristic perifascicular myofiber atrophy. The CD8+ T cells are believed to be important in the pathogenesis of
polymyositis. T cell–mediated myelin injury is seen with Guillain-Barré syndrome, causing an acute ascending paralysis.
Mutations in ion channel genes give rise to various channelopathies, including hypokalemic periodic paralysis and
malignant hyperthermia. Expansion of CTG repeats is seen with myotonic dystrophy.
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- 20.
A 71-year-old woman is receiving a drug to lower her serum cholesterol. Over the past week she has developed muscle pain and weakness unrelated to physical activity. On examination she has diffuse but mild muscle tenderness. Laboratory studies show her serum creatine kinase is 2049 U/L and creatinine 2 mg/dL. Urine dipstick analysis is positive for blood, without red blood cells on urine microscopy. Which of the following drugs is most likely to produce her findings?
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Atorvastatin
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Nicotinic acid
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Cholestyramine
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Ezetimibe
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Clofibrate
Correct Answer
A. AtorvastatinExplanation
(A) She has a statin-induced myopathy, with a creatine kinase level more than 10 times normal from rhabdomyolysis
(myoglobin causing renal tubular damage and detected by the dipstick). Statins are HMG CoA reductase inhibitors that
reduce endogenous cholesterol synthesis in liver. Cholestyramine binds bile acids in the intestine and disrupts
enterohepatic bile acid circulation to increase conversion of cholesterol to bile acids in the liver. Clofibrate enhances
uptake and oxidation of free fatty acids in muscle. Ezetimibe interferes with intestinal lipid absorption. Nicotinic acid inhibits
mobilization of peripheral free fatty acids to reduce hepatic triglyceride synthesis and secretion of VLDL.
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- 21.
A 10-year-old girl has exhibited muscular weakness since early childhood that has not worsened. She can ambulate unassisted, but does not participate in strenuous physical activities. On examination she has 4/5 motor strength in proximal muscles and 5/5 in distal muscles. There is no muscle pain on palpation. A biopsy of deltoid is obtained and shows subsarcolemmal aggregates of rod-shaped intracytoplasmic inclusions with Gomori trichrome stain. Laboratory studies show a normal serum creatine kinase. Which of the following is the most likely form of muscle disease she has?
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Channelopathy
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Congenital myopathy
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Glycogen storage disease
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Hereditary neuropathy
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Inflammatory myopathy
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Mitochondrial myopathy
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Muscular dystrophy
Correct Answer
A. Congenital myopathyExplanation
(B) She has nemaline rod myopathy, one form of congenital myopathy. The congenital myopathies may present in
infancy or childhood and may be non-progressive or slowly progressive. They are often named for their characteristic
histologic features. Channelopathies typically present as periodic paralysis with abnormalities in serum potassium. The
two glycogen storage diseases most often affecting striated muscle include Pompe disease (type II) and McArdle disease
(type V). There are increased glycogen deposits seen with periodic acid-Schiff (PAS) stain. Neuropathies affect muscle
through denervation, leading to groups of atrophic muscle fibers. Polymyositis and dermatomyositis are inflammatory
myopathies that are accompanied by myalgia and fiber degeneration with increased serum creatine kinase. Mitochondrial
myopathies may appear in childhood but are usually progressive, and often other organs such as heart or brain are
involved. Dystrophic muscle diseases lead to fiber degeneration with atrophy and fibrosis, with elevation in creatine
kinase; the most common muscular dystrophies involve dystrophin gene mutations that are X-linked.
BP8 829PBD7 1340PBD8 1271–1272Rate this question:
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.JPG "A 44-year-old man has had worsening exercise intolerance for the past year. On physical examination, he has 4/5
motor strength in the extremities, but has no muscle pain or loss of joint mobility. He has pitting edema to the knees. A
chest radiograph shows cardiomegaly with pulmonary edema and pleural effusions. A deltoid muscle biopsy specimen is
obtained. The figure shows the immunohistochemical staining pattern with antibody to dystrophin (A, normal; B, patient).
What is the most likely diagnosis?")
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Aug 20, 2012Quiz Created by
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