Motor neuron disease mimics in practice: a case series

In the majority of cases of motor neuron disease (MND), diagnosis is clinical and unambiguous. However, given the gravity of the diagnosis, it is crucial that treatable mimics are differentiated accurately. We present three cases referred to our clinic with possible MND with unusual features that led to an alternative diagnosis. (1) A middle-aged man with swallowing, then speech problems and foot drop. Tongue movements were slow and electromyography (EMG) showed fibrillations/positive sharp waves. Following investigation, a tonsillar tumour involving the tongue root was identified, and the foot drop improved, suggesting unrelated common peroneal nerve palsy (related to weight loss) or lumbar radiculopathy. (2) An elderly man presenting with progressive unilateral leg weakness and localised fasciculations on EMG. Following investigation, a high-grade brain glioma was diagnosed. (3) An elderly woman presenting with progressive quadriparesis over 18 months with fibrillations and chronic denervation on EMG. Symmetrical weakness and short duration response to immunotherapy led to further serological investigation and a diagnosis of anti-GD1a motor neuropathy. She was treated successfully with intravenous immunoglobulin, cyclophosphamide and rituximab and is now in remission.