For the past 4 months a previously healthy 37-year-old woman has noted increasing fatigue toward the end of the day. She does not have myalgia or arthralgia. She makes more mistakes while typing, and she can hardly keep her eyes open. She seems better in the morning after a good night's sleep. A month later she has difficulty swallowing and speaking. On physical examination she has 5/5 motor strength in extremities, but 4/5 after repetitive motion, with return to 5/5 after administration of edrophonium. Deep tendon reflexes are normal. Cranial nerves II - XII are intact. Which of the following pathologic abnormalities is most likely to be present in this woman?
A Anterior horn cell neuronophagia
B Loss of myelin
C Abnormal calcium channels
D Acetylcholine receptor degradation
E Myositis
F Vasculitis
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An 8-year-old boy gets tired easily and can be outrun by his 5-year-old brother. On physical examiantion he has 4/5 strength in lower extremities, even though his legs appear well-developed. Laboratory studies show his serum creatine kinase is 550 U/L. A gastrocnemious biopsy shows marked interstitial fibrosis with atrophy of many fibers and increase in size of others, but no inflammation. Immunohistochemical staining with antibody to dystrophin shows a lack of staining around the fibers. Over the next 5 years, he becomes progressively weaker until he is confined to a wheelchair. Which of the following inheritance patterns is his disease most likely to have?
A X-linked recessive
B X-linked dominant
C Autosomal dominant
D Multifactorial
E Autosomal recessive
A 29-year-old woman has had increasing muscular pain, particularly involving her upper arms and legs, not related to exercise, for the past year. She has had increasing difficulty swallowing for the past two months. Her fingers now often become blue and painful when exposed to cold. On physical examination she has a pale bluish-purple discoloration of her upper eyelids. She is afebrile. Which of the following light microscopic features is most likely to be present in a muscle biopsy from this woman?
A Myositis with lymphocytic infiltrates
B Grouped atrophy of fibers
C Extensive fibrosis and loss of fibers
D Absent dystrophin immunostaining
E "Ragged red fibers" with trichrome staining
F Increased glycogen deposits
A 47-year-old man has experienced progressive, symmetrical muscular weakness for the past 2 years. He has no myalgias or arthralgias. His mental status is unchanged. There is no history of traumatic injury. Within the past two months he has had increasing difficulty with swallowing and speaking. On physical examination, fasciculations of the tongue are noted. A deltoid biopsy is obtained. Which of the following microscopic findings involving myofibers is most likely to be seen?
A Grouped atrophy
B Inflammation
C Fibrosis
D Irregular variation in fiber size
E Fatty infiltration
F Degeneration with regeneration
G Central nuclei
A 45-year-old woman has noted increasing weakness for the past year, with greater difficulty climbing stairs or getting out of her car. She reports no myalgias. She has no difficulty typing. A physical examination reveals 4/5 motor strength in proximal muscule groups and 5/5 strength in distal muscle groups of extremities. An abdominal CT scan reveals a 2 cm mass in the right adrenal gland. A deltoid biopsy is performed and on microscopic examination shows myofiber atrophy, predominantly affecting type 2 fibers. Which of the following conditions is she most likely to have?
A Graves disease
B Lambert-Eaton syndrome
C Leigh syndrome
D Myotonic dystrophy
E Becker muscular dystrophy
F Cushing syndrome
A 19-year-old previously healthy university student finds it increasingly more difficult to climb the stairs to her dormitory room for the past 6 months. She now has difficulty getting out of a chair. She reports worsening myalgias. On physical examination, she has periorbital edema in addition to a violaceous skin rash that involves her upper eyelids. She has symmetric muscle weakness with only 3/5 strength in both upper and lower extremities. Labortory testing reveals that she has an HLA-DR3 phenotype. A gastrocnemious biopsy is performed. Which of the following microscopic findings is most likely to be present in this biopsy?
B Eosinophilic infiltrates
C Perivascular lymphocytes
D Type II fiber atrophy
E Increased glycogen deposits
A 68-year-old woman has had a 7 kg weight loss over the past 14 months from difficulty eating and swallowing. She is diagnosed with an esophageal carcinoma. She has increasing weakness. She dies from pneumonia. At autopsy, microscopic examination of skeletal muscle from this woman is most likely show which of the following findings?
A Degeneration and regeneration
B Necrosis
C Inflammation
D Metastasis
E Atrophy
Severe myalgia with fever are present in a 28-year-old man 3 weeks after he returned from a camping trip to Alaska. On that trip, he and his fellow travellers hiked extensively. They ate wild game they cooked themselves. On physical examination he has 4/5 proximal motor strength in extremities, with tenderness to palpation of large muscle groups. A CBC shows a total WBC count of 14,600/microliter, Hgb 14.8 g/dL, Hct 45.0%, MCV 93 fL, and platelet count 215,000/microliter. WBC differential count shows 66 segs, 5 bands, 10 lymphs, 7 monos, and 12 eos. His serum creatine kinase is 640 U/L. Which of the following findings is a muscle biopsy most likely to show?
B Encysted larvae
C Degeneration and regeneration
D Neutrophilic infiltrates
E Fibrosis
A 19-year-old man is involved a motorcycle accident in which he incurs a severe back injury with fracture-dislocation of C8. At the scene, it is noted on physical examination that he has no sensation in his lower chest down to his toes, and he cannot move his legs. A muscle biopsy is taken from his gastrocnemius a month later. Which of the following microscopic findings in the myofibers is most likely to be seen in this biopsy?
A Inflammation
B Central nuclei
C Grouped atrophy
D Fibrosis of myofibers
E Degeneration and regeneration
F Ring fibers
A 30-year-old man has exhibited slowly progressive muscle weakness over the past 5 years. He has no myalgias. He now has difficulty ambulating and picking up heavy objects, even though he used to be a weightlifter. On physical examination there is 4/5 motor strength in proximal muscle groups. Laboratory studies show a serum creatine kinase of 450 U/L. A deltoid biopsy is performed and on microscopic examination shows variation in fiber size; immunohistochemical staining shows only focal positivity for dystrophin around the fibers. Which of the following is the most likely diagnosis?
A Dermatomyositis
B Becker muscular dystrophy
C Werdnig-Hoffman disease
D Amyotrophic lateral sclerosis
E Poliovirus infection
F Myotonic dystrophy
A 50-year-old man has had progressive symmetrical muscle weakness for the past year. He reports no myalgia or arthralgia. Five years later, he is confined to bed. A year later he has difficulty speaking and swallowing. A deltoid biopsy is now performed and on microscopic examination demonstrates grouped atrophy of muscle fibers with no inflammation or myofiber necrosis. No other family members are similarly affected. His serum creatine kinase is 82 U/L. Through which of the following mechanisms is his disease most likely mediated?
A Myophosphorylase deficiency
B Denervation
C Dystrophy
D Autoimmunity
E Corticosteroid excess
F C5-9 membrane attack complex
A 25-year-old G2 P1 woman gives birth following an uncomplicated pregnancy to a term girl infant. She displays mild generalized muscular weakness. As she matures, the weakness remains mild and relatively nonprogressive. Her serum creatine kinase is 55 U/L and her antinuclear antibody test is negative. On physical examination her deep tendon reflexes are normal and there is no significant muscle wasting. The child does not have myalgias or arthralgias. She has normal mental function. Which of the following is the most likely etiology for her disease?
A Diminished dystrophin on muscle fibers
B Antibody against skeletal muscle proteins
C Congenital cytomegalovirus infection
D Congenital myopathy
E Deficiency of acid maltase
A 13-year-old boy fatigues easily and complains of cramping pain with exercise 'all over' after only a few laps around the track in his high school physical education class. If he rests briefly, he can continue for a few more laps. At rest, or with activities of daily living, he experiences no myalgias. One day, the coach makes him continue much longer, and he notes passing dark urine an hour later. On physical examination he has normal range of motion and agility, with no evidence for muscle wasting. Muscle strength is 5/5 in all extremities. Deep tendon reflexes are 2+. Laboratory studies show an absence in elevation of blood lactate, but an increase in blood ammonia, following exercise. Which of the following laboratory test findings is most characteristic for his underlying disease?
A Increased serum creatine kinase
B Oligoclonal bands in the CSF
C Eosinophilia
D Hypercortisolemia
E Myoglobinuria
Hours after consuming a meal that included home-canned peas, a man and his wife began to develop weakness and progressive respiratory failure 3 hours later. On physical examination they have 3/5 motor strength in all extremities. Deep tendon reflexes are normal. They are afebrile. Which of the following infectious diseases are they most likely to have?
A Salmonellosis
B Botulism
C Diphtheria
D Gas gangrene
E Tetanus
F Polio
A 9-year-old girl notes that, as long as she can remember, she gets tired easily. She is still able to perform nomal daily activities. Through young adulthood, she continues to exhibit mild generalized muscle weakness. On physical examination, she has motor strength 4/5 in all extremities along with hypotonia. Reflexes are normal. She has no myalgias. A deltoid biopsy is performed and on microscopic examination shows muscle fibers with numerous rod-shaped intracytoplasmic inclusions. Which of the following conditions is most likely to produce the findings seen in this patient?
A Autoimmune disease
B Lower motor neuron disease
C Muscular dystrophy
E Myophosphorylase deficiency
F Parasitic infection
A 35-year-old woman had a diagnosis of polymyositis made with a muscle biopsy. Following a course of corticosteroid therapy, she continues to have muscular weakness, particularly involving proximal muscles. Her serum creatine kinase (CK) is only 41 U/L. An electromyogram demonstrates no myopathic changes. Which of the following is the most likely diagnosis?
A Treatment failure
B Upper motor neuron disease
C Corticosteroid-induced myopathy
D McArdle disease
E Duchenne muscular dystrophy
A 42-year-old man has had increasing muscular weakness over the past 2 years, with both his arms and legs mainly affected. Other men and women in his family have been similarly affected. He has such severe difficulty chewing his food that he is on a liquid diet. His eyelids droop so much that he can no longer drive a vehicle. On physical examination he has symmetrical muscle atrophy, most marked in hands and forearms, and of the sternocleidomastoids. Deep tendon reflexes, sensation, and cranial nerve function are intact. A muscle biopsy is performed and on microscopic examination shows myofiber atrophy, mainly of type I fibers, with central nuclei and ring fibers. Genetic testing reveals a mutation with increased CTG repeats. Which of the following is the most likely diagnosis?
A Duchenne muscular dystrophy
B Myotonic dystrophy
D Becker muscular dystrophy
E McArdle disease
F Leigh syndrome
A 7-year-old child suddenly becomes more irritable and complains of a headache and neck pain. Three weeks later, her parents note that she now appears listless and has difficulty getting up and moving about. Physical examination reveals 4/5 motor strength in her lower extremities along with hyporeflexia, but sensation is intact. She remains mentally alert. She exhibits no seizure activity. Laboratory studies show Hgb 13.3 g/dL, Hct 40%, MCV 93 fL, platelet count 297,000/microliter, and WBC count 5520/microliter with 65 segs, 3 bands, 19 lymphs, 9 monos, 2 eosinophils, and 2 basophils. Her serum creatine kinase is 20 U/L. A gastrocnemius biopsy is performed and on microscopic examination shows grouped myofiber atrophy. Which of the following infectious agents is most likely to cause her findings?
A Cytomegalovirus
B Rabies virus
C Herpes simplex virus
D Echovirus
E Poliovirus
F Varicella-zoster virus
For the past 4 years, a 55-year-old man has fatigued easily as the day progresses, but after a night's rest feels better in the morning. At first, he noted that his eyelids drooped, but now he has difficulty chewing food, particularly meat (with the exception of Kobe beef). Physical examination reveals 4/5 motor strength in both right and left extremities. Deep tendon reflexes are normal. A gastrocnemius biopsy is performed and on microscopic examination shows no major histologic abnormalities. Which of the following is the most likely diagnosis?
A Myasthenia gravis
B Duchenne muscular dystrophy
C Trichinosis
D Werdnig-Hoffman disease
E Amyotrophic lateral sclerosis
A 50-year-old man had experienced progressive, symmetrical muscular weakness over the past 4 years. At first, he had difficulty climbing stairs. Two years later he was confined to a wheelchair. Another two years passed and he could no longer feed himself. Which of the following microscopic findings is most likely to be seen in a muscle biopsy from this man?
A Atrophy of all muscle fibers with fibrosis
B Grouped atrophy of muscle fibers
C Type II fiber atrophy
D Inflammation with necrosis
E Minimal, intermittent staining for dystrophin
A 22-year-old woman has had progressive symmetrical muscular weakness along with diffuse myalgias for the past 2 months. She has had dysphagia for the past week. On physical examination she has 3/5 motor strength in proximal muscles of all extremities. A gastrocnemious biopsy is performed and on microscopic examination shows neutrophils and lymphocytes with destruction of individual myofibers. Which of the following is the most likely diagnosis?
B Polymyositis
A 3-year-old girl has had increasing weakness involving all of her extremities since birth. Her parents indicate that she has had no major illnesses. She was a term birth without complications. She has no fever. Laboratory findings, including a CBC, chemistry panel, and urinalysis, are unremarkable. A gastrocnemious biopsy is performed and shows grouped atrophy of myofibers without inflammation, necrosis, or regeneration. Which of the following is the most likely diagnosis?
A Leigh syndrome
B Werdnig-Hoffman disease
C Duchenne muscular dystrophy
D Central core disease
E Pompe disease
F Nemaline myopathy
A 10-year-old girl has developed increasing weakness over the past year. She has no muscle pain or atrophy. She has epilepsy. Other family members are affected as shown by this pedigree:
On physical examination she exhibits ataxia. A gastrocnemious biopsy is performed and on microscopic examination shows increased numbers of ragged red fibers. She suffers a "stroke" at age 20. Which of the following conditions is she most likely to have?
A Mitochondrial myopathy
C Channelopathy
E Lambert-Eaton syndrome
A 25-year-old woman has had episodes of myalgia involving nearly every major muscle group of her extremities for the past 2 months. She also has chest pain. On physical examination she is afebrile. Her lungs are clear on auscultation but there is dullness to percussion. She has no joint deformities. Laboratory studies show her antinuclear antibody test and double stranded DNA test are positive. She has pericardial and pleural effusions seen on a chest CT scan. Which of the following findings is she most likely to have on microscopic examination of a muscle biopsy?
B Increased glycogen deposition
E No significant changes
A 29-year-old man has had a mild respiratory tract infection with non-productive cough and fever for the past 3 days. Over the next 2 days he has decreased urine output, and his urine has a dark brown color. On physical examination he has muscle tenderness. Laboratory studies show his serum urea nitrogen is 39 mg/dL with creatinine 4.1 mg/dL and creatine kinase 621 U/L. A urinalysis shows sp gr 1.025, pH 6, and blood 4+, with negative protein, glucose, and ketones. Urine microscopic examination shows no casts, no WBCs, and no RBCs. Which of the following microscopic findings is most likely to be present in a muscle biopsy from this man?
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