Anti-ganglioside antibodies (Abs) are implicated as primary immune effectors in acute motor axonal neuropathy (AMAN) and Fisher syndrome (FS) variants of Guillain-Barré syndrome (GBS). Besides affecting peripheral nerve axons, anti-ganglioside Abs may also target distal portions of motor axons including neuromuscular junction (NMJ). It has been reported that antiganglioside Abs can bind to NMJs and thereby exert a variety of pathophysiological effects in animal models. However, it is unknown whether anti-ganglioside Abs can cause clinical NMJ disease in human. We are reporting a rare case of NMJ disorder as a clinical manifestation of anti-ganglioside Abs (Anti GD-1a and Anti GM1) in a patient with newly diagnosed lung cancer.

A 39-year-old Male smoker presented with three-month history of progressive proximal and bulbar muscle weakness. Exam showed weakness in head flexion/extension and proximal muscle, decreased respiratory mechanics. Neuro-imaging and CSF studies were normal. He initially responded well to the treatment with Mestinon and Intravenous Immunoglobulin (IVIG). Work ups including Acetylcholine receptor antibodies, anti-MusK antibody, and antibody to presynaptic voltage-gated calcium channels were negative. However, serum anti-ganglioside GD1a/ GM1 Abs, checked prior to IVIG treatment, were significantly and consistently increased (3 to 4 folds). Nerve Conduction Study/Repetitive Nerve Stimulation showed pathological decrement of Compound Muscle Action Potential (CMAP) more than 10% suggesting of NMJ disorder. One month later, CT chest showed lung mass and biopsy revealed Squamous Cell Carcinoma. This patient has been stable with monthly IVIG therapy.

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