Small cell lung cancer found through a disabling paraneoplastic neuropathy

What happened, in summary

A 69-year-old woman developed worsening weakness in her arms and legs, loss of balance, and declining hand function. Nerve-conduction studies confirmed a predominantly sensory axonal polyneuropathy. Intravenous immunoglobulin and pulsed corticosteroids did not improve her symptoms, and she eventually needed a walking frame and help adapting her home.

Extensive investigation found anti-CRMP5 antibodies, raising concern for a paraneoplastic neurological syndrome. Routine chest CT did not show a lung mass. PET imaging, however, identified a suspicious solitary lymph node in the chest. Mediastinal biopsy confirmed small cell lung carcinoma confined to that node. The cancer was classified as T0N2M0, with an occult lung primary and no distant metastasis.

She received carboplatin and etoposide over four weekly cycles, followed by 30 fractions of radiation therapy. She completed both treatments without major treatment complications, although fatigue was substantial and her neurological symptoms worsened temporarily during chemotherapy.

After treatment, she entered monthly oncology follow-up with plans to move to three-monthly review. Preventive brain radiation was being assessed, and further CT and PET imaging were planned to evaluate the cancer response. Physiotherapy and home exercises continued, but her hand dexterity, walking, and independence had improved little. She remained positive and focused on rehabilitation, supported closely by her husband and daughters. The case shows how a severe paraneoplastic neuropathy can precede detection of a very small, otherwise hidden small cell lung cancer.