Occult bowel cancer presenting as Morvan syndrome

A man in his mid-60s presented with a 3-month history of progressive muscle twitching, agitation, cognitive impairment, insomnia, hyperhidrosis and lower limb pain. He had fasciculations, myokymia, myoclonus, exaggerated startle response and significant postural hypotension. Electrophysiological studies showed evidence of peripheral nerve hyperexcitability with neuromyotonia. Contactin-associated protein-like 2 antibodies (CASPR2) were strongly positive. A diagnosis of Morvan syndrome was made. CT of the chest, abdomen and pelvis was undertaken to identify any occult malignancy, and a large bowel carcinoma in situ was identified and resected. His central nervous system and autonomic symptoms significantly improved following surgery, but neuromyotonia persisted, and this was treated with intravenous immunoglobulins and steroids. Early detection of bowel cancer in this patient enabled curative treatment.