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

A 50-year-old man is seen for a new-patient evaluation. He reports a recent diagnosis of Parkinson disease made after a 2-year history of stiffness in his right arm, a tendency to posture when walking, an awkward and stiffly inverted step when using the right leg, but no tremor. During this period, his voice became softer and slightly high pitched.

The patient lost his sense of smell 10 years ago and has a 2-year history of diplopia when reading, a 9-month history of urinary urgency and impotence, and no history of dementia, depression, or psychosis. He has been taking high-dose levodopa replacement therapy since diagnosis without improvement in symptoms.

Which of the following features in the patient’s history is most suggestive of an atypical parkinsonism syndrome?

A: Absence of a tremor
B: Diplopia
C: Impotence
D: Loss of olfaction
E: Poor response to levodopa

MKSAP Answer and Critique

The correct answer is E: Poor response to levodopa. This item is available to MKSAP 16 subscribers as item 3 in the Neurology section.

MKSAP 16 released Part A on July 31. More information is available online.

The sign most suggestive of an atypical parkinsonism syndrome in this patient is the absence of response to high-dose levodopa replacement. Parkinson disease remains a clinical diagnosis that is based on a cardinal set of clinical features, including resting tremor, bradykinesia, rigidity, and postural instability; the tremor, bradykinesia, and rigidity are asymmetric. Sustained levodopa responsiveness is expected in Parkinson disease and helps confirm the clinical diagnosis. All patients with suspected parkinsonism should have an adequate trial of levodopa. A lack of response indicates that the neurodegenerative process extends substantially beyond the nigrostriatal pathway and involves other basal ganglion structures. In the absence of a standard, convenient, readily affordable diagnostic test for Parkinson disease, the diagnosis depends on the response to levodopa.

The absence of a tremor should raise the suspicion of atypical parkinsonism, although tremor is absent in up to 30% of patients with classic idiopathic Parkinson disease, as confirmed by autopsy. Therefore, the absence of a tremor is less suggestive of an atypical parkinsonism syndrome than is the lack of response to levodopa replacement.

Convergence insufficiency is a common finding in patients with Parkinson disease, causing diplopia while reading, and is not suggestive of atypical parkinsonism.

Many patients with Parkinson disease have autonomic dysfunction, including constipation, urinary urgency and incontinence, impotence, orthostasis, and temperature instability. Therefore, the presence of impotence in this patient does not exclude Parkinson disease as a diagnosis. When autonomic symptoms are especially severe and overshadow the motor signs of the disorder, further autonomic testing may be indicated, and a diagnosis of the atypical parkinsonism syndrome of multiple system atrophy, autonomic type, may be made.

The absence of olfaction is a frequent finding in Parkinson disease, sometimes preceding the onset of motor signs by many years, and has not been associated with atypical parkinsonism syndromes.

Key Point

• Absence of a response to levodopa is most suggestive of an atypical parkinsonism syndrome.

Learn more about ACP’s MKSAP 16.

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