Polymyositis masquerading as motor neuron disease.

BACKGROUND

Several conditions have been reported to mimic motor neuron disease (MND), and misdiagnosis remains a common clinical problem.

OBJECTIVE

To report a case of bulbar-onset polymyositis where the initial clinical presentation was suggestive of MND.

CASE DESCRIPTION: A 73-year-old woman was admitted for investigation of acute-onset dysphagia without dysarthria. Examination revealed nasal dysphonia and severe oropharyngeal weakness. Subtle upper-limb weakness, brisk tendon reflexes, and fasciculations in the right deltoid muscle were also demonstrated. A clinical diagnosis of MND was entertained. The serum creatine kinase value was within the reference range. Findings from electromyographic studies, however, were suggestive of a myopathic rather than a neurodegenerative process, and a muscle biopsy specimen was diagnostic of polymyositis. The dysphagia rapidly resolved upon treatment with corticosteroids and azathioprine.

CONCLUSIONS

Bulbar-onset polymyositis may mimic MND, particularly in the absence of inflammatory markers or elevated muscle enzyme levels. Caution should be exercised in the clinical diagnosis of bulbar dysfunction, and further investigations such as electromyography and muscle biopsy are indicated to confirm the diagnosis.