Lambert-Eaton myasthenic syndrome

A 64-year-old man presented with proximal lower limb muscle weakness that had ascended over 3 months to involve the upper limb, bulbar and periocular muscles. In addition, he had muscle aches, dry eyes and mouth, with 10 kg of weight loss. He was an ex-smoker of 50 pack-years. On examination, he had mild dysarthria, bilateral ptosis and proximal muscle weakness (MRC power 4/5) in all limbs that improved transiently after muscle use. All limb tendon reflexes were absent at rest but returned after sustained muscle contraction for 10 seconds. The serum voltage-gated calcium-channel antibody titre was 237 pmol/litre (normal <45 pmol/litre). High frequency repetitive nerve stimulation (Figure 1) produced a successive increase in compound muscle action potential amplitude, confirming the diagnosis of Lambert–Eaton myasthenic syndrome. On spiral computed tomography there was a pretracheal mass extending into the right paratracheal region (Figure 2). Tissue biopsy confirmed small cell lung carcinoma.