Paraneoplastic Morvan's syndrome following surgical treatment of recurrent thymoma: A case report

Morvan's syndrome (MoS) is a rare, complex neurological disorder characterized by neuromyotonia, neuropsychiatric features, dysautonomia and neuropathic pain. The majority of MoS cases have a paraneoplastic aetiology, usually occurring prior to the diagnosis of the underlying tumour and showing improvement following its treatment. The present study reports the case of a 35‑year‑old Caucasian male patient who was diagnosed with stage IVA thymoma. Thymectomy, lung resection, diaphragmatic pleurectomy and pericardio‑phrenectomy were performed 6 months after neoadjuvant chemotherapy. The pathological evaluation revealed a type B2‑B3 thymoma with focal squamous differentiation. Two years later, the patient underwent new surgical treatment for a local recurrence of the same histological type, and 4 weeks later, the patient presented with complex neurological symptoms compatible with MoS, including neuromyotonia, neuropsychiatric features, dysautonomia and neuropathic pain. Electromyography was compatible with a diagnosis of neuromyotonia. Brain magnetic resonance imaging scan and tests for serum anti‑acetylcholine receptor, anti‑striated muscle antibodies and anti‑30‑kDa titin fragment antibodies were all negative, whereas tests for anti-voltage-gated potassium channel (VGKC)‑complex antibodies (333.3 pmol/l), anti‑leucine‑rich glioma inactivated protein 1 and anti-contactin-associated protein‑like 2 antibodies were positive. The patient underwent 3 cycles of intravenous administration of immunoglobulins (0.4 g/kg/day for 5 days every 4 weeks) with little clinical and electrophysiological improvement. We speculated that the late onset of the symptoms in the present patient may have been triggered by an increase in the serum level of anti‑VGKC antibody, which was caused by the surgery performed for the treatment of recurrent thymoma. To the best of our knowledge, the present report is the first case of MoS associated with this histological type of thymoma uncommonly occurring upon surgical treatment of recurrent thymoma.