Data from: Isaacs syndrome associated with GABAB and AChR antibodies in sarcomatoid carcinoma

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.