Pathology Review Ch 27

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Pathology Review Ch 27 - Quiz


Questions and Answers
  • 1. 

    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?

    • A.

      Serum acetylcholinesterase antibody titer

    • B.

      Immunohistochemical staining for dystrophin

    • C.

      Eosinophil count in blood

    • D.

      Presence of oligoclonal bands of immunoglobulin in cerebrospinal

    • E.

      PCR to detect expansion of CGG repeats on Xq27.3

    Correct Answer
    B. Immunohistochemical staining for dystrophin
    Explanation
    (B) The onset of muscle weakness in childhood suggests an inherited muscular dystrophy. The biopsy specimen shows
    variation in muscle fiber size and increased connective tissue between the fibers. This morphologic finding in a boy
    strongly suggests X-linked muscular dystrophy. Immunohistochemical staining for dystrophin would show an absence of
    dystrophin, confirming the diagnosis of Duchenne muscular dystrophy. Antibodies to the acetylcholine receptor are found
    in myasthenia gravis, which is characterized by weakness in muscles after repetitive use. Eosinophilia may be present in
    allergic or parasitic disorders, including trichinosis. Oligoclonal immunoglobulin bands in the cerebrospinal fluid are a
    feature of multiple sclerosis. Expansion of CGG repeats on Xq27.3 is diagnostic of familial mental retardation.
    BP7 780–782BP8 827–828PBD7 1336–1338PBD8 1268–1269

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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?

    • A.

      Repetitive stress injury

    • B.

      Diabetes mellitus

    • C.

      Amyotrophic lateral sclerosis

    • D.

      Acute intermittent porphyria

    • E.

      Varicella-zoster virus infection

    Correct Answer
    A. Repetitive stress injury
    Explanation
    (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.
    BP7 847PBD7 1335PBD8 1266–1267

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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?

    • A.

      Guillain-Barré syndrome

    • B.

      Cerebral astrocytoma

    • C.

      Cerebral infarction

    • D.

      Diabetes mellitus

    • E.

      Multiple sclerosis

    Correct Answer
    D. Diabetes mellitus
    Explanation
    (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.
    BP7 847BP8 784–785, 898PBD7 1334PBD8 1265–1266

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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?

    • A.

      Duchenne muscular dystrophy

    • B.

      Polymyositis

    • C.

      Poliomyelitis

    • D.

      Trichinosis

    • E.

      Diabetes mellitus

    Correct Answer
    D. Trichinosis
    Explanation
    (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.
    BP7 312, 780BP8 327PBD7 407–408PBD8 393

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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?

    • A.

      Amyotrophic lateral sclerosis

    • B.

      Duchenne muscular dystrophy

    • C.

      McArdle disease

    • D.

      Myasthenia gravis

    • E.

      Myotonic dystrophy

    • F.

      Werdnig-Hoffmann disease

    Correct Answer
    F. Werdnig-Hoffmann disease
    Explanation
    (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.
    BP7 216BP8 827, 897PBD7 1336PBD8 1267

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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?

    • A.

      Guillain-Barré syndrome

    • B.

      Multiple sclerosis

    • C.

      Amyotrophic lateral sclerosis

    • D.

      Varicella-zoster virus infection

    • E.

      Vitamin B12 (cobalamin) deficiency

    Correct Answer
    A. Guillain-Barré syndrome
    Explanation
    (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.
    BP7 848BP8 899PBD7 1331PBD8 1261–1262

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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?

    • A.

      Elevated serum creatine kinase level

    • B.

      Acetylcholine receptor antibody positivity

    • C.

      Peripheral blood eosinophilia

    • D.

      Increased serum cortisol level

    • E.

      Antihistidyl tRNA synthetase (anti-Jo-1) titer 1 : 512

    Correct Answer
    B. Acetylcholine receptor antibody positivity
    Explanation
    (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.
    BP7 115, 779–780BP8 125, 830PBD7 1344PBD8 1275–1276

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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?

    • A.

      Chronic hepatitis C

    • B.

      Duchenne muscular dystrophy

    • C.

      Small-cell lung carcinoma

    • D.

      Lead poisoning

    • E.

      Diabetes mellitus

    Correct Answer
    C. Small-cell lung carcinoma
    Explanation
    (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.
    BP7 780BP8 830PBD7 1344–1345PBD8 1276

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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?

    • A.

      Cushing syndrome

    • B.

      McArdle disease

    • C.

      Duchenne muscular dystrophy

    • D.

      Myasthenia gravis

    • E.

      Polymyositis

    Correct Answer
    A. Cushing syndrome
    Explanation
    (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.
    BP7 779BP8 826PBD7 1209, 1344PBD8 1260

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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?

    • A.

      Werdnig-Hoffmann disease

    • B.

      Polymyositis

    • C.

      Becker muscular dystrophy

    • D.

      Amyotrophic lateral sclerosis

    • E.

      Myasthenia gravis

    • F.

      Myotonic dystrophy

    Correct Answer
    C. Becker muscular dystrophy
    Explanation
    (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.
    BP7 780–782BP8 827–828PBD7 1336–1338PBD8 1268–1269

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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?

    • A.

      Calcium ion channel

    • B.

      Motor end plate

    • C.

      Oxidative phosphorylation enzyme

    • D.

      Sarcoglycan complex

    • E.

      Thick filament

    Correct Answer
    A. Calcium ion channel
    Explanation
    (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.
    BP8 829PBD7 1340PBD8 1270

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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?

    • A.

      Aging

    • B.

      Diabetes mellitus

    • C.

      Multiple sclerosis

    • D.

      Somatoform pain disorder

    • E.

      Vitamin B12 (cobalamin) deficiency

    • F.

      Varicella-zoster virus infection

    Correct Answer
    F. Varicella-zoster virus infection
    Explanation
    (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.
    BP8 877PBD7 1332PBD6 1262–1263

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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?

    • A.

      Wallerian degeneration

    • B.

      Acute inflammation

    • C.

      Onion bulb formation

    • D.

      Endoneurial lymphocytic infiltration

    • E.

      Axonal neuropathy

    Correct Answer
    E. Axonal neuropathy
    Explanation
    (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.
    BP7 847BP8 784–785, 898PBD7 1334PBD8 1265–1266

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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?

    • A.

      Werdnig-Hoffmann disease

    • B.

      Amyotrophic lateral sclerosis

    • C.

      Becker-type muscular dystrophy

    • D.

      Myasthenia gravis

    • E.

      Mitochondrial myopathy

    Correct Answer
    B. Amyotrophic lateral sclerosis
    Explanation
    (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.
    BP7 778–779BP8 827, 896PBD7 1335, 1396–1397PBD8 1324–1325

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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?

    • A.

      1 day

    • B.

      1 week

    • C.

      1 month

    • D.

      1 year

    Correct Answer
    D. 1 year
    Explanation
    (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.
    BP7 847BP8 898PBD7 1329–1330PBD8 1259–1260

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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?

    • A.

      Diabetes mellitus type 1

    • B.

      Diabetes mellitus type 2

    • C.

      Entrapment neuropathy

    • D.

      Lead poisoning

    • E.

      Thiamine deficiency

    • F.

      Vitamin B12 (cobalamin) deficiency

    • G.

      Wallerian degeneration

    Correct Answer
    C. Entrapment neuropathy
    Explanation
    (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.
    BP7 847PBD7 1335PBD8 1267

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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?

    • A.

      Abnormal voltage-gated calcium channel

    • B.

      Antibodies to acetylcholine receptor

    • C.

      Cytotoxic CD8+ lymphocytes

    • D.

      Decreased sarcolemmal dystrophin

    • E.

      Deficient mitochondrial enzyme

    • F.

      Increased CTG repeat sequences at 19q13.2–13.3

    Correct Answer
    E. Deficient mitochondrial enzyme
    Explanation
    (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.
    BP7 15, 235–236BP8 829PBD7 1341–1342PBD8 1271–1273

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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?

    • A.

      Appearance of acute inflammation around the graft

    • B.

      Formation of a traumatic neuroma

    • C.

      Grouped atrophy of facial muscles

    • D.

      Growth of recurrent tumor along the nerve graft

    • E.

      Wallerian degeneration in the distal facial nerve

    Correct Answer
    E. Wallerian degeneration in the distal facial nerve
    Explanation
    (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.
    BP7 847BP8 898PBD7 1329–1330PBD8 1258–1260

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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?

    • A.

      Myofiber injury by CD8+ T cells directed against muscle antigens

    • B.

      T cell–mediated peripheral nerve injury induced by Mycoplasma pneumoniae infection

    • C.

      Antibody- and complement-mediated injury to the microvasculature

    • D.

      Mutation in a gene encoding for voltage-gated calcium channels

    • E.

      Expansion of CTG repeat sequences on chromosome 19q13.2

    Correct Answer
    C. Antibody- and complement-mediated injury to the microvasculature
    Explanation
    (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.
    BP7 143–144BP8 151PBD7 1342–1343PBD8 1273–1275

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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?

    • A.

      Atorvastatin

    • B.

      Nicotinic acid

    • C.

      Cholestyramine

    • D.

      Ezetimibe

    • E.

      Clofibrate

    Correct Answer
    A. Atorvastatin
    Explanation
    (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.
    PBD8 1275

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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?

    • A.

      Channelopathy

    • B.

      Congenital myopathy

    • C.

      Glycogen storage disease

    • D.

      Hereditary neuropathy

    • E.

      Inflammatory myopathy

    • F.

      Mitochondrial myopathy

    • G.

      Muscular dystrophy

    Correct Answer
    B. Congenital myopathy
    Explanation
    (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 1271–1272

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  • Jun 22, 2023
    Quiz Edited by
    ProProfs Editorial Team
  • Aug 20, 2012
    Quiz Created by
    Chachelly
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