Neurophysiology is part of a Neurologist's armamentarium. There are instances, however, when nerve conduction studies and electromyography does not represent the patient's clinical features and may, in turn, lead us away from the correct diagnosis.
We present a rare case of peripheral nerve hyperexcitability, which was initially diagnosed as motor neuron disease based on neurophysiological findings. This had repercussions for the patient's prognosis and management of his initial symptoms.
The patient was a 70 year old gentleman who presented with weakness, fasciculations, weight loss and difficulty in breathing. On further questioning he also had insomnia, hyperhidrosis, dysaesthetic pain in both legs and pruritis affecting his feet. His fasciculations were global including his face. He had diminished reflexes which improved with repetitive exercise.
CT thorax revealed a thymoma and his sera was positive for AChR antibodies, negative for MUSK, VGCC and VGKC antibodies.
Incidentally the patient was treated for an exacerbation of COPD with steroids which improved his symptoms, including fasciculations, confirming an antibody mediated phenomenon.
The final diagnosis is therefore more in keeping with a paraneoplastic Morvan's syndrome secondary to thymoma and not Motor Neuron disease.