There is a lack of clear classification systems for non-progressive, benign lower motor neuron syndromes of the upper limb, resulting in misdiagnosis of motor neuron disease (MND) at first presentation. Appropriate investigation and identification of distinguishing features is required to reduce this risk.Methods
A retrospective analysis of 91 patients with an atypical presentation of a pure lower motor neuron weakness and/or wasting of the upper limb was performed. These were divided into final diagnostic categories and disease onset, progression and investigations were compared to identify features more indicative of benign disease. In addition, we assessed whether flexion-extension MRI was performed appropriately to investigate for Hirayama disease, a benign cervical flexion myelopathyDiscussion
24.2% of the cohort had benign disease, 45.1% developed MND. Features more predictive of a diagnosis of MND at initial presentation were bilateral arm involvement (OR 15.6, p=0.002), upper limb fasciculations (OR 29.07, p<0.001) and acute EMG changes outside of the cervical region (OR 17.5, p=0.001). Acute denervation within the cervical region did not distinguish between benign disease and MND. Flexion-extension MRI was performed in 17.8% of cases meeting the criteria for Hirayama Disease, indicating a lack of awareness or consideration of this condition.