Neuromuscular Disorders Flashcards
- A 65-year-old man was diagnosed with lung cancer 6 months ago. Over the last 2 months, he has had worsening severe proximal muscle weakness. He is most likely to have which of the following?
a. Dermatomyositis
b. Trichinosis
c. Multiple sclerosis (MS)
d. Progressive multifocal leukoencephalopathy (PML)
e. Myasthenia gravis
A
(Victor, p 1484.) Dermatomyositis occurs as a paraneoplastic syndrome in about 15% of cases overall. Among those over age 40, the proportion of paraneoplastic cases increases to 40% for women and 66% for men. Tumors underlying dermatomyositis may develop in the lungs, ovaries, gastrointestinal tract, breasts, or other organs, but the CNS is generally not the site of a tumor associated with dermatomyositis. Because of the higher probability of malignancy in adults with dermatomyositis, patients diagnosed with this inflammatory disease should routinely undergo a variety of diagnostic studies, including rectal and breast examinations, periodic screens for occult blood in the stool, and hemograms. Sputum cytologies and chest x-rays, as well as urine cytologic studies, are recommended by some physicians. Both PML and MS are strictly CNS diseases. Trichinosis is a parasitic disease that involves skeletal muscle and may produce substantial weakness but is not associated with any tumors.
- The rash typically associated with this man’s condition is characterized by which of the following?
a. Adenoma sebaceum
b. Shagreen patches
c. Target-shaped erythematous lesions on the extremities
d. A purplish discoloration around the eyes
e. Telangiectasias
D
(Victor, p 1483.) The violaceous, or purplish, discoloration developing around the eyes is called a heliotrope rash (after the flower that has similar coloring). These patients also have erythema over the knuckles. A target-shaped lesion on the limb suggests Lyme disease. Adenoma sebaceum and shagreen patches are skin changes typical of tuberous sclerosis. Telangiectasias over the malar eminences, conjunctivae, and ears occur with ataxia telangiectasia.
A 67-year-old woman has noticed blurry vision and weakness over the past 4 months. Her symptoms are always worse toward the end of the day. She undergoes a neuromuscular evaluation including electromyography, and the diagnosis of myasthenia gravis is made.
- The most obvious site of disease in myasthenia gravis is the
a. Anterior horn cell
b. Neuromuscular junction
c. Sensory ganglion
d. Parasympathetic ganglia
e. Sympathetic chain
B
(Rowland, pp 721–726.) Myasthenia gravis is a disease—or, more accurately, a collection of diseases—in which autoimmune damage occurs at the neuromuscular junction. The postsynaptic membrane is damaged in myasthenia gravis, and the acetylcholine receptor is the principal site of damage. A relative acetylcholine deficiency develops at the synapse because receptors are blocked or inefficient. Symptoms of
A 67-year-old woman has noticed blurry vision and weakness over the past 4 months. Her symptoms are always worse toward the end of the day. She undergoes a neuromuscular evaluation including electromyography, and the diagnosis of myasthenia gravis is made.
- The most common manifestation of muscle weakness with myasthenia gravis is
a. Diaphragmatic weakness
b. Wristdrop
c. Footdrop
d. Ocular muscle weakness
e. Dysphagia
D
(Rowland, p 723.) More than 90% of patients with myasthenia gravis have some type of ocular motor weakness. This ranges from ophthalmoplegia to lid ptosis. Patients usually notice the lid weakness or complain of blurred vision as one of the first symptoms. More severe disease includes limb weakness, difficulty with swallowing, and respiratory difficulties. Patients usually report fatigue that increases as the day progresses.
- A 28-year-old woman has the clinical diagnosis of myopathy and undergoes a muscle biopsy for diagnosis. The pathology demonstrates an inflammatory muscle disease characterized by noncaseating granulomas. Which of the following may have caused her symptoms?
a. Cysticercosis
b. Tuberculosis
c. Sarcoidosis
d. Schistosomiasis
e. Carcinomatosis
C
(Victor, pp 1490–1491.) Sarcoidosis is a poorly understood inflammatory disease that may cause neuropathy as well as myopathy. Multiple organs are usually involved with sarcoidosis, with hepatic or pulmonary disease often the most consistent finding. The non-caseating granulomas help to distinguish sarcoidosis from tuberculosis, a similar disease with an established infectious basis that usually produces caseating granulomas.
- A 62-year-old woman complains of limb discomfort and trouble getting off the toilet. She is unable to climb stairs and has noticed a rash on her face about her eyes. On examination, she is found to have weakness about the hip and shoulder girdle. Not only does she have a purplish-red discoloration of the skin about the eyes, but she also has erythematous discoloration over the finger joints and purplish nodules over the elbows and knees. Which of the following is the most probable diagnosis?
a. Systemic lupus erythematosus
b. Psoriasis
c. Myasthenia gravis
d. Dermatomyositis
e. Rheumatoid arthritis
D
(Victor, pp 1482–1488.) This woman presents with proximal muscle weakness and pain and a heliotrope rash about her eyes. The term heliotrope refers to the lilac color of the periorbital rash characteristic of dermatomyositis. This rash surrounds both eyes and may extend onto the malar eminences, the eyelids, the bridge of the nose, and the forehead. It is usually associated with an erythematous rash across the knuckles and at the base of the nails and may be associated with flat-topped purplish nodules over the elbows and knees. Men with dermatomyositis are at higher than normal risk of having underlying malignancies. Psoriatic arthritis may be associated with reddish discoloration of the knuckles and muscle weakness, but the heliotrope rash would not be expected with this disorder. The age of onset for a psoriatic myopathy is also atypical. Similarly, the patient’s rashes are not suggestive of lupus erythematosus, although a myopathy may occur with this connective tissue disease as well.
- Duchenne muscular dystrophy is a sex-linked disorder involving the gene responsible for the synthesis of
a. Glucose-6-phosphatase
b. Hexosaminidase B
c. Myosin
d. Dystrophin
e. Actin
D
(Bradley, p 2193.) Duchenne dystrophy has been incontrovertibly linked to the gene, located on the X chromosome, that makes dystrophin. The more profound the disturbance of this gene, the earlier the disease becomes symptomatic. The gene for dystrophin has single or multiple deletions in affected children. Women who are probable carriers of the defective gene can be checked for heterozygosity and given genetic counseling. Chorionic villus biopsy at 8 to 9 weeks can determine if a fetus that is at risk for the deletion actually carries it.
A 32-year-old woman has several family members with Duchenne dystrophy. She has genetic testing and is known to be a carrier of the gene.
- A blood test may exhibit substantial elevations in her serum of which of the following?
a. Ammonia
b. Myoglobin
c. Phosphofructokinase
d. Creatine phosphokinase (CPK)
e. Hexosaminidase
D
(Rowland, p 738.) A high CPK in a woman with male relatives affected by Duchenne dystrophy indicates a high probability that she is a carrier of the abnormal dystrophin gene. A normal CPK, however, does not rule out the possibility that the woman is a carrier of Duchenne dystrophy. Even an asymptomatic carrier of the gene may have abnormalities in limb girdle muscles on biopsy.
A 32-year-old woman has several family members with Duchenne dystrophy. She has genetic testing and is known to be a carrier of the gene.
- Duchenne dystrophy affects approximately
a. 1 in 3,000 infants
b. 1 in 3,000 male infants
c. 1 in 30,000 infants
d. 1 in 30,000 male infants
e. 1 in 50,000 infants
B
(Rowland, pp 737–739.) Duchenne muscular dystrophy is a fairly common cause of childhood disability, but it is limited to boys. The disease is progressive, but the progression is over the course of years rather than weeks. Affected children rarely survive past adolescence. The incidence of the defect in male fetuses is greater than that in male infants because affected male fetuses have a higher rate of spontaneous abortion than do unaffected male fetuses in families carrying the abnormal gene.
A 32-year-old woman has several family members with Duchenne dystrophy. She has genetic testing and is known to be a carrier of the gene.
- For a female child to have Duchenne dystrophy, she must have
a. Turner syndrome (XO)
b. Klinefelter syndrome (XXY)
c. Two affected parents
d. An affected father
e. An affected brother
A
(Rowland, pp 737–739.) Duchenne dystrophy may occur in the person with Turner syndrome if the inherited X chromosome carries the defective dystrophin gene. In the absence of a normal X chromosome, only the defective dystrophin will be produced. The person with Turner syndrome has only one X chromosome but is phenotypically female. Duchenne dystrophy may occur in girls with two X chromosomes if translocations of material from the normal X chromosome inactivate or eliminate the normal dystrophin gene.
A 32-year-old woman has several family members with Duchenne dystrophy. She has genetic testing and is known to be a carrier of the gene.
- The spontaneous mutation rate for the dystrophin gene is presumed to be high because
a. Men with Duchenne dystrophy do not reproduce
b. The incidence of Duchenne dystrophy is increasing
c. Numerous birth defects occur in families with Duchenne dystrophy
d. Men may become symptomatic after adolescence
e. Genetic studies of eggs in human ovaries reveal an excess of abnormal dystrophin genes
A
(Rowland, pp 737–739.) Despite the drain from the population of males carrying the abnormal gene, the incidence of Duchenne dystrophy is stable. Males often die before they reach sexual maturity or are too impaired after adolescence to mate. There are no changes in the ovaries of women bearing a child with Duchenne dystrophy to suggest that the mutation is arising de novo in the ovary. Women with apparently normal dystrophin genes do, however, give birth to affected sons.
- Intellectual function in children with Duchenne dystrophy is usually
a. Markedly impaired
b. Slightly impaired
c. Normal
d. Slightly better than that of the general population
e. Markedly superior to that of the general population
B
(Rowland, pp 738–739.) Although profound mental retardation is not typical with Duchenne dystrophy, children with the disease characteristically perform more poorly than their unaffected siblings on objective cognitive tests. Persons with the Becker variant, the much milder form of the dystrophy that usually becomes symptomatic during adult life, may have no perceptible cognitive impairments. Women carrying the gene have normal cognitive abilities.
- With Duchenne dystrophy, pseudohypertrophy routinely
a. Does not occur
b. Is limited to the shoulder girdle
c. Is limited to the hip girdle
d. Is limited to the calf muscles
e. Is limited to the thigh muscles
D
(Rowland, pp 738–739.) The calves are usually enlarged in the child with Duchenne dystrophy. Other clinical characteristics include a lordotic posture as weakness evolves in the hip girdle musculature. The gait becomes waddling before the child is unable to walk at all. Affected children invariably exhibit the Gower sign at some time in the evolution of their weakness: the child gets up from the floor by using his hands to walk up his legs and trunk to achieve an upright posture.
- A 37-year-old man has difficulty relaxing his grip on his golf club after putting. He also complains of problems with excessive somnolence. Examination reveals early cataract development, testicular atrophy, and baldness. His family notes that he has become increasingly stubborn and hostile over the past 3 years. His electrocardiogram (ECG) reveals a minor conduction defect. An electromyogram (EMG) will probably reveal
a. Repetitive discharges with minor stimulation
b. Polyphasic giant action potentials
c. Fasciculations
d. Fibrillations
e. Positive waves
A
(Bradley, p 2209.) Men with myotonic dystrophy characteristically exhibit problems with relaxing their grip, hypersomnolence, premature baldness, testicular atrophy, and cataracts. The EMG pattern displayed by these patients is often referred to as the dive bomber pattern because of the characteristic sound produced when the evoked action potentials are heard. The cardiac defect that evolves in these persons usually requires pacemaker implantation to avoid sudden death. Psychiatric problems also develop in many patients with myotonic dystrophy, but their basis is unknown.
- A 75-year-old man has malaise and slowly progressive weight loss for the better part of 3 months. Laboratory tests reveal a hematocrit of 32%, an erythrocyte sedimentation rate (ESR) of 97 mm/h, and a white blood cell (WBC) count of 10,700 cells per µL. Serum CPK and thyroxine (T4) levels are normal. Which of the following is the most likely explanation for the patient’s complaints?
a. Polymyositis
b. Dermatomyositis
c. Polymyalgia rheumatica
d. Rheumatoid arthritis
e. Hyperthyroid myopathy
C
(Victor, p 1572.) The markedly elevated sedimentation rate, anemia, weight loss, and malaise in a person of this age suggest polymyalgia rheumatica, although the same complaints in someone 20 years younger could not be explained on the basis of this disorder. Fever may also be evident in the affected person. This constellation of symptoms also suggests an occult neoplasm or infection, and investigations should be conducted to reduce the likelihood of overlooking one of these diseases. Polymyalgia rheumatica is an arteritis of the elderly and is improbable in someone less than 60 years of age. The normal CPK activity markedly reduces the likelihood that this myalgia is the result of polymyositis or dermatomyositis. The new onset of rheumatoid arthritis at this age is also improbable. A hyperthyroid myopathy in the face of a normal T4 level is possible on the basis of an elevated T3 level, but it is also much less likely than polymyalgia rheumatica in this age group.
