Superior oblique palsy as the initial manifestation of anti-contactin-1 IgG4 autoimmune nodopathy: A case report

Autoimmune nodopathy (AN) is a group of peripheral neuropathies caused by antibodies targeting the nodes of Ranvier or paranodes. It typically presents with sensory ataxia, distal limb weakness, and tremor, and often has a subacute onset, with limited response to immunoglobulin or corticosteroids. We report a case of anti-contactin-1 neuropathy initially manifesting as isolated superior oblique palsy, aiming to broaden the clinical spectrum of the disease. A 68-year-old male with well-controlled diabetes, hypertension, and hyperlipidemia developed acute binocular vertical diplopia, progressing over two months to include distal paresthesia, sensory ataxia, ageusia, and dysarthria. Concurrent nephrotic syndrome was identified. Nerve conduction studies supported demyelination. Despite treatment with intravenous methylprednisolone followed by long-term immunosuppression, some disability persisted. Serum archived during his admission tested positive for anti-contactin-1 IgG, with IgG4 as the predominant subclass, in the flow cytometry assay for AN. This case extends the clinical spectrum of AN. Some cases of isolated cranial nerve palsies, especially in the relevant context like nephrotic syndrome, may be attributed to AN. Prompt initiation of more effective therapies, such as rituximab, could significantly improve outcomes.