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Diabetic cranial mononeuropathy — SCE Endocrinology MCQ

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HardDiabetes complicationsDiabetic cranial mononeuropathySCE Endocrinology

A 58-year-old man with long-standing type 2 diabetes develops sudden painful diplopia. Examination shows ptosis with the eye deviated down and out, but the pupil is spared. HbA1c is 82 mmol/mol and blood pressure is 158/92 mmHg. What is the most likely diagnosis?

Educational content. Not a substitute for clinical judgement or local policy.

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Correct answer: D — Diabetic microvascular third nerve palsy

Diabetic microvascular third nerve palsy is best because painful pupil-sparing third nerve palsy in a patient with vascular risk factors is typical of diabetic microvascular ischaemia. The alternatives are less appropriate because aneurysm classically threatens the pupil; myasthenia is variable; thyroid eye disease causes restrictive orbitopathy; cavernous sinus thrombosis has sepsis and multiple cranial nerve signs. The SCE teaching point is to integrate the clinical pattern, biochemistry and context rather than treating an isolated result.

Reference: NICE NG28; neuro-ophthalmology guidance