Type 2 Respiratory Failure as an Initial Manifestation of Lambert-Eaton Myasthenic Syndrome Complicated by Paraneoplastic Autoimmune Encephalitis.

Lambert-Eaton myasthenic syndrome (LEMS) is a paraneoplastic or autoimmune neuromuscular disorder that typically presents with limb weakness or autonomic dysfunction. Here, we report a rare case of LEMS with acute type 2 respiratory failure as the initial symptom. A 79-year-old woman was admitted with acute disturbance of consciousness and type 2 respiratory failure. On admission, she presented with confusion, seizures, and respiratory acidosis requiring non-invasive positive pressure ventilation. Cerebrospinal fluid analysis revealed pleocytosis and elevated protein levels without infection. Electroencephalography showed nonspecific slowing, while imaging revealed no abnormalities. A nerve conduction study on day 10 confirmed LEMS, with findings of low-amplitude compound motor action potentials and facilitation on high-frequency stimulation. Coexisting autoimmune encephalitis was diagnosed based on clinical presentation and serum antibody positivity for voltage-gated calcium channels and gamma-aminobutyric acid B receptors. Positron emission tomography/CT identified small-cell lung cancer, confirmed by biopsy. The patient and family declined invasive cancer therapies. Then, the patient passed away on day 60. This case highlights the diagnostic challenge of atypical presentations of paraneoplastic neurological syndromes, including LEMS and autoimmune encephalitis. Early recognition of LEMS in patients with unexplained type 2 respiratory failure through nerve conduction studies is critical. This report underscores the importance of considering paraneoplastic etiologies in patients with multiple neurological syndromes.