Neuromuscular Disorder Flashcards
1
Q
- 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 gravi
A
- The answer is 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.
2
Q
- 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
A
- The answer is 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.
3
Q
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.
328. 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 chai
A
- The answer is 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
myasthenia gravis range from slight ocular motor weakness to ventilatory
failure.
4
Q
329. The most common manifestation of muscle weakness with myasthenia gravis is a. Diaphragmatic weakness b. Wristdrop c. Footdrop d. Ocular muscle weakness e. Dysphagia
A
- The answer is 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
5
Q
- 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
A
- The answer is 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 noncaseating
granulomas help to distinguish sarcoidosis from tuberculosis, a
similar disease with an established infectious basis that usually produces
caseating granulomas
6
Q
- 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
A
- The answer is 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
7
Q
332. 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
A
- The answer is 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
Neuromuscular Disorders Answers 229
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.
8
Q
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.
333. 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
A
- The answer is 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.
9
Q
- 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
A
- The answer is 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
10
Q
- 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
- The answer is 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
11
Q
- 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
- The answer is 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
12
Q
- 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
A
- The answer is 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.
13
Q
- 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
A
- The answer is 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.
14
Q
- 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
- The answer is 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.
15
Q
- 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
A
- The answer is 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
Neuromuscular Disorders Answers 231
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.
