IntroductionLambert Eaton myasthenic syndrome (LEMS) is a neuromuscular junction transmission disorder that is associated with malignancy (most often small cell lung cancer) and antibodies to the voltage gated calcium channel. Rarely, it can occur as a non-paraneoplastic phenomenon. The diagnosis can be difficult, and reduced motor amplitudes on nerve conduction studies can be misattributed to neurogenic or myopathic processes unless the referring physician or neurophysiologist considers LEMS in the differential diagnosis. Two cases of non-paraneoplastic LEMS were identified from testing performed in the Neurophysiology laboratory of St Vincent’s Hospital Melbourne in 2017. The histories, examination findings, investigations, extensive neurophysiological testing and response to treatment are presented.CasesThe two patients identified were aged 18 and 34 years at diagnosis. Both had a history of slowly progressive proximal weakness preferentially affecting the lower limbs over several years, with associated autonomic symptoms. The younger patient had become wheelchair dependent at age 17. Detailed neurophysiological testing demonstrated a pre-synaptic defect of neuromuscular junction transmission. The younger patient showed myopathic features on needle EMG. Voltage gated calcium channel antibodies were positive in both cases. Treatment with intravenous immunoglobulin, 3, 4-diaminopyridine, pyridostigmine, and azathioprine was associated with a definite improvement in strength and function in both patients. The patient with myopathic EMG features has residual moderate weakness but is now ambulant. Extensive screening for malignancies (including whole-body PET) has been negative, but surveillance will be continued for up to 5 years.ConclusionNon-paraneoplastic LEMS is a rare, but treatable, condition that warrants consideration, particularly when neurophysiological testing reveals reduced motor amplitudes. Successful diagnosis requires a threshold of suspicion in the neurophysiologist or referring neurologist.
Voltage‐gated calcium channel nanodomains: molecular composition and function
