Abstract Details

Title A Case of Lambert Eaton Myasthenic Syndrome with Cerebellar Ataxia Complicated by Encephalopathy and Confounded by Generalized Pain

Topic Neuromuscular and Clinical Neurophysiology (EMG)

Presentation(s) P6 - Poster Session 6 (5:30 PM-6:30 PM)

Poster/Presentation
Number 11-009

Background Lambert-Eaton myasthenic syndrome (LEMS) is a neuromuscular junction disorder caused by the generation of antibodies against presynaptic voltage-gated calcium channels (VGCC). Clinical features include proximal muscle weakness with areflexia, autonomic dysfunction, and post-exercise facilitation, characterized by the return of tendon reflexes and muscle strength with repeated muscle contraction. Patients with cerebellar ataxia and LEMS have been described in the literature with associated VGCC antibodies.

Objective Objective: To present a case of Lambert Eaton Syndrome, initially misdiagnosed as fibromyalgia, with subsequent development of encephalopathy and cerebellar ataxia.

Design/Methods Case report and literature review.

Results A 62-year-old man with a 30-year smoking history presented with six months of extremity pain with weakness, muscle fatigue, imbalance, and dysarthria. Twenty days later, he worsened with the additional development of diplopia. Exam demonstrated mild dysarthria, 4/5 weakness in upper and lower extremities, and global areflexia. Electrodiagnostic studies demonstrated reduced amplitudes in all motor nerves, 60-90% increase in amplitudes after 10 seconds of exercise, and a decrement with 3 Hz repetitive stimulation. Serum VGCC Abs tested positive. His hospital course was complicated by severe encephalopathy. After treatment with amifampridine, prednisone, and plasma exchange, his condition stabilized. Following a course of IVIG, he improved enough to be safely discharged home. Severe axial and appendicular ataxia were noted after discharge. Increasing amifampridine helped his strength but not the ataxia; repeat IVIG is scheduled. A whole-body PET revealed a benign appearing axillary node, with biopsy results pending.

Conclusions Pain is a feature of LEMS. Patients with LEMS often endorse weakness out of proportion to exam findings due to post-exercise facilitation, which can lead to misdiagnosis. Low amplitude CMAPs serve as the first clue distinguishing LEMS from Myasthenia Gravis and should prompt investigation of facilitation. This case adds to the rare but reported cases of LEMS with encephalopathy and LEMS co-existing with cerebellar ataxia.

Authors/Disclosures
Marissa Urbano, MD PRESENTER	Dr. Urbano has nothing to disclose.
Sandeep Singh, MD	Dr. Singh has nothing to disclose.
Antonio Moya, MD (Rancho Los Amigos Rehabilitation)	Dr. Moya has nothing to disclose.
Margaret Adler, MD (Harbor UCLA Department of Neurology)	Dr. Adler has nothing to disclose.