Objective:

To report a case of peripheral nervous system hyperexcitability syndrome associated with thymic carcinoma and positive paraneoplastic antibodies.

Background:

Peripheral nerve hyperexcitability syndromes are rare neurological disorders often linked to autoimmune mechanisms, including antibodies targeting voltage-gated potassium channels (VGKC) and associated proteins such as CASPR2 and LGI1. These syndromes can manifest as muscle twitching, cramps, and fasciculations, which can significantly affect the patient's quality of life. The association of these syndromes with thymic carcinoma is uncommon but notable in this case.

Design/Methods:

n/a

Results:

A 46-year-old African-American woman with a history of sarcoidosis and left breast cancer presented with 5 months history of muscle twitching, cramps, and spasms predominantly in the extremities and face following an upper respiratory infection. The symptoms were intermittent and worsened with physical activity. Neurological examination revealed tongue atrophy, fasciculations, and widespread muscle twitching, notably in the right calf and left forearm. Laboratory tests showed positive CASPR2, LGI1, and VGKC antibodies, while EMG confirmed fasciculations and myokymia without signs of neuropathy. Imaging revealed a thymic mass, which was later confirmed as thymic carcinoma. Initial treatment with IVIG provided minimal improvement, but after five cycles of plasmapheresis, the patient experienced significant symptom relief. The patient subsequently underwent thymic mass resection.

Conclusions:

This case illustrates a rare instance of peripheral nerve hyperexcitability associated with thymic carcinoma and positive paraneoplastic antibodies. Timely diagnosis and management with immunotherapy and surgical resection can lead to significant improvement in symptoms, emphasizing the importance of considering paraneoplastic syndromes in similar clinical presentations.