ID 210 – Overlapping respiratory neuromuscular dysfunction in a case of Lambert–Eaton syndrome

Abstract

Background Respiratory failure is a multifactorial and common complication among patients with small cell lung cancer (SCLC). Phrenic nerve injury secondary to local invasion or diaphragmatic neuromuscular junction (NMJ) disorder associated to Lambert–Eaton Syndrome (LES) may occasionally be involved. Objective To report a case of diaphragmatic dysfunction secondary to combined phrenic nerve injury and presynaptic NMJ transmission failure in a 50-year-old man with SCLC. Methods/Results The electrophysiological findings fulfilled the criteria of and P/Q-type VGCC antibodies were highly positive (343 pmol/l). On admission, the phrenic nerve conduction studies disclosed a markedly reduced CMAP amplitude with postactivation facilitation on the right side. The response was absent on the left with profuse spontaneous activity on diaphragmatic needle EMG. Follow-up study reported favorable response to treatment with 3,4-diaminopyridin on the right side. No changes were observed on the left, suggesting a persistent phrenic nerve injury. Conclusions Respiratory electrophysiological studies are invaluable tools to distinguish between many possible causes of respiratory dysfunction in patients with lung cancer and should be routinely included as part of a diagnostic work up. Key message Neuromuscular respiratory involvement in patients with SCLC may be overlooked. Abnormally very low diaphragm CMAP amplitudes should arise suspicion for presynaptic NMJ disorder.