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Polymyositis Masquerading as Motor Neuron Disease
Aisling Ryan, MRCPI, PhD;
Azli M. Nor, MRCPI;
Donal Costigan, MB;
Daragh Foley-Nolan, FRCPI;
Ahmed El-Rafie, MRCPI;
Michael A. Farrell, FRCPI;
Orla Hardiman, MD, FRCPI
Arch Neurol. 2003;60:1001-1003.
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.
From the Departments of Neurology (Drs Ryan, Nor, and Hardiman) and Neuropathology (Dr Farrell), National Institute for Neurology and Neurosurgery, Beaumont Hospital, and the Neurophysiology Laboratory (Dr Costigan), Dublin, Ireland; and the Department of Rheumatology (Drs Foley-Nolan and El-Rafie), Waterford Regional Hospital, Waterford, Ireland.
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