LAUSR

Isaacs syndrome is an acquired peripheral nerve hyperexcitability syndrome characterized by twitching, painful cramps, stiffness, delayed muscle relaxation, and sweating.1 Needle EMG findings include continuous single motor unit discharges occurring as doublets, triplets, and multiplet single unit discharges firing at higher rates (150–300 Hz; neuromyotonic discharges) and at lower rates (less than 60 Hz; myokymic discharges).2 Isaacs syndrome has been reported in patients with thymoma, small-cell lung carcinoma (SCLC), or lymphoma.2 Antibodies specific for voltage-gated potassium channels (VGKC) have been reported as a serologic marker of Isaacs syndrome. Antibodies specific for the neuronal ganglionic acetylcholine receptor (AChR) are sometimes encountered in some patients.1 It has not been previously associated with sarcomatoid carcinoma (SC) or antibodies against γ-aminobutyric acid B (GABAB) receptors, and the latter often present in limbic encephalitis and other uncommon clinical syndromes (such as cerebellar ataxia).3 Here we describe a case of Isaacs syndrome with a positive test for anti-GABAB and anti-AChR antibodies and broad tumor screening for this case of SC.