Test your medicine knowledge with the MKSAP challenge, in partnership with the American College of Physicians.

A 65-year-old man is evaluated for worsening gait unsteadiness and falls. He first noticed the unsteadiness 1 year ago while walking and has started to fall recently, falling four times in the past 2 weeks. Approximately 3 years ago, he developed erectile dysfunction and has had increasing constipation ever since that time.

On physical examination, vital signs are normal except for the supine blood pressure, which is 190/105 mm Hg; blood pressure decreases to 76/50 mm Hg when he stands without a compensatory increase in the pulse rate. Results of mental status testing are normal. He has mildly slurred speech. Testing of cranial nerve function, including testing of extraocular movements, reveals no abnormalities. Manual muscle strength in the upper and lower extremities is normal, but he has mild rigidity of the extremities and mild appendicular ataxia. His gait is slow with a reduced stride length and arm swing, and he has marked postural instability.

Which of the following is the most likely diagnosis?

A) Dementia with Lewy bodies
B) Multiple system atrophy
C) Parkinson disease
D) Progressive supranuclear palsy

MKSAP Answer and Critique

The correct answer is B) Multiple system atrophy. This item is available to MKSAP 15 subscribers as item 22 in the Neurology section. More information about MKSAP 15 is available online.

Multiple system atrophy is the most likely diagnosis in this patient. He has a progressive neurologic disorder characterized by signs and symptoms that suggest impairment of multiple neurologic systems; these include the autonomic nervous system (orthostatic hypotension, erectile dysfunction, constipation), the extrapyramidal system (rigidity, impaired gait), and the cerebellum (limb ataxia). Multiple system atrophy is a progressive, ultimately fatal neurodegenerative disorder that typically causes dysautonomia, parkinsonism, and ataxia, in some combination, in affected patients. Multiple system atrophy is a clinical diagnosis that is suggested by the presence of these various features in the same patient.

Dementia with Lewy bodies is also typically associated with parkinsonian features and should be considered in the differential diagnosis of this patient. Dementia with Lewy bodies is associated with cognitive impairment, parkinsonian signs and symptoms, and possible evidence of dysautonomia. However, gait or limb ataxia is not expected, and the degree of dysautonomia typically is not as severe as that seen in multiple system atrophy.

The prominent dysautonomia, early falls, absence of a resting tremor, and presence of appendicular ataxia in this patient argue against Parkinson disease as the diagnosis. Early multiple system atrophy can, however, be difficult to distinguish from Parkinson disease, especially because some affected patients may respond initially to carbidopa-levodopa, a medication used to treat parkinsonian symptoms in Parkinson disease.

Progressive supranuclear palsy should also be part of the differential diagnosis in this patient. A rare neurodegenerative disorder, progressive supranuclear palsy is associated with parkinsonian signs and early falls due to marked postural instability. However, significant dysautonomia and ataxia are not expected. Marked impairment in vertical gaze is a hallmark of progressive supranuclear palsy.

Key Point

• Multiple system atrophy is a sporadic, heterogeneous, neurodegenerative disorder that causes impairment of multiple neurologic systems, including the autonomic nervous system, the extrapyramidal system, and the cerebellum.

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