Recognizing CA LEMS in Small Cell Lung Cancer: Clinical Features, the Classic Triad, and Cancer Screening Before Diagnosis

Dr. Primdahl describes what CA LEMS looks like clinically for oncologists with limited exposure to this diagnosis. Patients are unlikely to self-report proximal weakness in clinical terms; they more commonly describe difficulty with everyday tasks, such as climbing stairs, getting in and out of a car or chair. The classical clinical triad of CA LEMS is proximal lower-extremity weakness (legs more than arms), autonomic dysfunction (dry mouth, constipation, blurry vision from impaired pupillary function, erectile dysfunction), and hyporeflexia or areflexia. Important complicating overlaps include steroid-induced myopathy (also proximal but without autonomic features), CNS involvement from brain or leptomeningeal metastases, and chemotherapy-induced neuropathy (typically distal and sensory, opposite to LEMS). Any neurological symptom, particularly ocular or bulbar involvement such as swallowing difficulty or double vision, should prompt low-threshold referral to neurology or serologic screening.

CA LEMS can predate an SCLC diagnosis: approximately 50% to 60% of patients diagnosed with LEMS will eventually be found to have an underlying malignancy, most commonly SCLC. When neurologists identify LEMS without a known cancer diagnosis, cancer screening with CT chest, abdomen, and pelvis or FDG-PET/CT is initiated. Given the strength of the association, repeat imaging every approximately 3 months is recommended for at least 2 years even with initially negative imaging, particularly in high-risk patients (smokers, age over 50 years, weight loss). The DELTA-P score is a validated clinical tool that quantifies malignancy risk in newly diagnosed LEMS and guides screening intensity and duration accordingly.

Dr. Shields adds her practical bedside clinical test: asking patients to stand from a chair without holding the arms. Difficulty doing so signals proximal leg weakness and should prompt further investigation.