Paraneoplastic Neuromyotonia
A 70-year-old man with coronary artery disease, chronic obstructive pulmonary disease, and a 40-pack-year smoking history presented to a neurologist with a 2-month history of muscle twitching and spasms, excessive sweating, and a 10-kg weight loss. The physical examination revealed myokymia (involuntary, undulating muscle twitching) and fasciculations. Myokymia worsened with exercise and persisted during sleep. There was no muscle weakness, rigidity, atrophy, or delayed muscle relaxation after contraction. Needle electromyography showed characteristic neuromyotonic and myokymic discharges. Serologic testing for antibodies against the voltage-gated potassium channel complex was positive (396 pmol per liter; normal value, <85). On the basis of clinical, electromyographic, and serologic findings, neuromyotonia was diagnosed. In this condition, hyperexcitability of peripheral-nerve axons results in continuous activation of muscle fibers. Treatment with carbamazepine was initiated but was ineffective in controlling the symptoms. Because neuromyotonia may be paraneoplastic, and given the patient’s smoking history and marked weight loss, diagnostic evaluation for cancer was performed. Ultimately, biopsy of an enlarged supraclavicular lymph node revealed metastatic small-cell lung cancer. The patient died 3 months later from complications of chemotherapy.
Oh didn't concider how the muscle would be affected. It was from elevated electrolytes (and hyponatremia if SIADH), or somehow aberant Ab production?