The collapsin response-mediator protein-5 (CRMP5) autoantibody is a recognised biomarker for small cell lung cancer associated neurological Paraneoplasia.

We describe a 79-year-old lady, who presented with right hemi-chorea. This progressed over one month, becoming bilateral and rendering the patient bedbound.

MRI revealed bilateral signal change within the caudate and lentiform nuclei. CT chest detected mediastinal lymphadenopathy, while PET identified pulmonary malignancy with radiological staging T1bN3M0. Serum CRMP5 antibodies were positive.

Haloperidol and intravenous methylprednisolone lead to some improvement in Chorea and mobility. However, visual acuity deteriorated to finger counting. Fundoscopy revealed mild cataracts, while visual evoked potentials were very delayed on the right and absent on the left, suggesting optic neuropathy.

She deteriorated with leg pain, weakness, and loss of tendon reflexes, as well as cognitive decline and visual hallucinations. Clinically this raised suspicion of radiculoneuropathy and encephalopathy respectively. Whilst retaining capacity the patient refused further investigations and treatment. She was discharged to a nursing home and died 6 months later.

CRMP5 antibodies, targeting intracellular antigens, precipitate an onconeuronal autoimmune process through mechanisms not fully understood. We report a case of combined chorea, optic neuropathy, peripheral neuropathy, and encephalopathy, which highlights the potential for CRMP5 to cause multifocal neurological dysfunction.