Brachial Diparesis due to Motor Neuronopathy as One of the Predominant Presenting Signs of Occult Small Cell Lung Carcinoma.

Sensory neuronopathy is a well-established presentation in paraneoplastic neurological syndromes that is mostly associated with small cell lung cancer and anti-Hu antibodies. Motor neuronopathy, on the other hand, is an extremely rare observation in this syndrome. A 56-year-old man presented with asymmetric brachial diparesis and sensory ataxia. Electrophysiological studies revealed sensory ganglionopathy and progressive anterior horn degeneration in cervical segments. Small cell lung carcinoma with associated anti-Hu antibodies was later diagnosed. The patient did not improve despite the administration of steroids and chemotherapy. Paraneoplastic syndromes may exceptionally present with a bilateral arm weakness. Cases accompanied by sensory ganglionopathy should therefore be promptly investigated for any underlying malignancy.