A 64-year-old man reported bilateral, progressive and painless loss of vision affecting the left eye (OI) for 7 days and which in the last 48 hours had also started to affect the right eye (OD). The patient had a history of heavy smoking and the death of a brother due to pulmonary neoplasia. Ophthalmological examination revealed corrected visual acuity of 0.4 in the right eye and hand movement in the left eye. Intraocular pressure and anterior segment were normal, and funduscopy revealed moderate vitritis in both eyes, with slight hyperemia of the papilla in the OD, and papillary pallor in the OI. It was decided to admit the patient for further investigation, with the initial diagnosis of papillitis with bilateral vitritis.

The neurological examination, blood count and biochemistry were normal. The chest X-ray showed a slight thickening of the right pulmonary hilum, and the cranial CT scan was normal. Lumbar puncture showed only a discrete elevation of proteins. Based on these findings, it was decided to start treatment with corticosteroid boluses and antiplatelet therapy.

Angiofluoresceinography showed hypercapitation in the papilla with no signs of vasculitis. Evoked potentials were normal in OD and compatible with axonal neuropathy in OI. Electroretinogram and brain MRI were normal. Serology, immunology and usual tumour markers were negative.
Based on the tests obtained, an infectious, vascular or demyelinating aetiology was ruled out, so an infiltrative aetiology or a paraneoplastic syndrome was assessed. A thoracic-abdominal CT scan was requested, which showed a 3 cm image in the right hilum, compatible with adenopathy. Bronchoscopy showed a widening of the carina, and cytology was negative for malignancy. A PET study was proposed to better assess the lymphadenopathy and a referral to thoracic surgery for mediastinoscopy. In addition, samples of cerebrospinal fluid, plasma and aqueous humour were taken to study the CRMP-5-IgG autoantibody, which was positive in the first two samples. CRMP-5-IgG positivity and the presence of neuritis is associated in 62.5% of cases with the existence of a small cell lung carcinoma (2,3).

Based on these data, it was decided to cancel the PET study and perform a mediastinoscopy, which was reported as a microcytic lung carcinoma. The oncology department classified it as limited-stage microcytic carcinoma and started treatment with chemotherapy and radiotherapy.
The initial response to corticosteroid treatment was good, improving vision to 0.7-0.3 at 15 days and reaching a final visual acuity at six months, when we considered the study closed, of 0.8 in OD and 0.6 in OI, with an ad integrum restitution of the funduscopic image.