Acquired neuromyotonia heralding recurrent thymoma in myasthenia gravis.

IMPORTANCE: Acquired neuromyotonia is increasingly recognized as an autoimmune disorder, frequently associated with antibodies against voltage-gated potassium channel complex proteins.We present a case of acquired neuromyotonia as the heralding symptom of recurrent thymoma in a patient with myasthenia gravis. OBSERVATIONS: A report of a single case of a 53-year-old man with myasthenia gravis and a prior thymectomy presenting with 2 months of diffuse, involuntary muscle twitching in the absence of myasthenic symptoms, electrophysiologically confirmed to be neuromyotonia. Further evaluation revealed the recurrence of malignant thymoma, accompanied by refractory arrhythmia. Serologic and cerebrospinal fluid testing confirmed the presence of antibodies directed against 2 voltage-gated potassium channel–associated proteins: LGI1 and Caspr2. CONCLUSIONS AND RELEVANCE: This case highlights the overlap of myasthenia, neuromyotonia, and thymoma, emphasizing the importance of appropriate tumor screening in the presence of either of the former 2 conditions.