Lambert–Eaton Myesthenic Syndrome and Brain Metastasis from Occult Small Cell Lung Carcinoma: A Clinician’s Perspective

Lambert–Eaton myasthenic syndrome (LEMS) is a rare autoimmune disorder of neuromuscular transmission characterized clinically by muscle weakness, hyporeflexia or areflexia, and autonomic dysfunction. LEMS can occur as a remote effect of a neoplasm, in the paraneoplastic form (PLEMS), usually in association with small cell lung cancer (SCLC), or in the non-paraneoplastic form (NPLEMS). To denote a case as a patient with non-paraneoplastic LEMS needs a long-term follow up as in paraneoplastic cases where neurological symptoms can precede the diagnosis of primary neoplasm. Brain metastases from small cell lung cancer (SCLC) are found in approximately 10–14% of cases at presentation, with 65–95% of these cases also having disease outside the central nervous system (CNS) on diagnosis or shortly after. A solitary brain metastasis with an undetected primary is a rare presentation in cases of SCLC. Sometimes combinations of paraneoplastic syndromes (PS) and metastatic features might be the only presentation of the underlying occult primary SCLC. Certain clinical features together with relevant investigation help to clinch the diagnosis which has significant therapeutic implications in patients with occult primary SCLC. This chapter presents varied clinical features, diagnostic modalities, and therapeutic options in patients with LEMS and brain metastasis arising from occult primary SCLC. The authors also share their experience of a case of PLEMS and solitary cerebellar metastasis occurring simultaneously in the absence of a florid picture of SCLC.