A 28-year-old man presents with sudden onset of horizontal diplopia and inward deviation of the left eye for 2 days. He has a history of uncontrolled diabetes mellitus. On examination, the left eye is adducted, and there is limitation of abduction. Pupillary responses are normal and brisk. The fundus is normal. What is the most appropriate next step in management?

Explanation

## Clinical Diagnosis This is a case of **sixth cranial nerve (abducens) palsy** secondary to **diabetes mellitus**. The key features are: - Sudden onset horizontal diplopia - Inward deviation of left eye (due to unopposed medial rectus action) - Limitation of abduction (abducens nerve function) - Normal pupils (ruling out third nerve palsy) - Diabetes as a risk factor ## Management of Acquired Sixth Nerve Palsy **High-Yield:** In an adult with acute sixth nerve palsy and a clear vasculopathic risk factor (diabetes, hypertension, age >50), the management is **conservative** with observation and symptomatic relief, NOT immediate neuroimaging. **Key Point:** Vasculopathic (microvascular) sixth nerve palsies in diabetics have a high spontaneous recovery rate (>90%) within 3–6 months. Immediate MRI is reserved for: - Younger patients (<50 years) without vasculopathic risk factors - Bilateral nerve palsies - Progressive or worsening palsy - Pupillary involvement (suggesting third nerve pathology) - Red flags for mass or demyelination ## Recommended Management Sequence 1. **Symptomatic relief:** Prism glasses to relieve diplopia and improve quality of life 2. **Optimize glycemic control:** Essential to promote nerve recovery 3. **Observation:** Serial examinations at 4–6 week intervals 4. **Reassess at 3 months:** If no improvement, consider imaging (MRI) to rule out structural lesion 5. **Surgery:** Reserved for cases with persistent palsy after 6–12 months (if recovery does not occur) **Clinical Pearl:** Prism glasses provide immediate symptomatic relief by realigning the visual axes and eliminating diplopia. They are the first-line symptomatic treatment for acute nerve palsies while awaiting spontaneous recovery. **Mnemonic: VASCULAR-6** — **V**asculopathic risk (diabetes, HTN, age), **A**cute onset, **S**pontaneous recovery expected (>90%), **C**onservative management, **U**se prisms for diplopia, **L**ong observation period (3–6 months), **A**void early surgery, **R**ecover usually complete. ## Why Not Immediate MRI? In a 28-year-old with diabetes and acute sixth nerve palsy: - Vasculopathic palsies are common in diabetics - Spontaneous recovery is expected - MRI is NOT indicated unless red flags are present (progressive symptoms, pupillary involvement, bilateral palsies, or failure to recover by 3 months) - Unnecessary imaging delays symptomatic management ## Why Not Immediate Surgery? Surgery is NOT appropriate in acute nerve palsies because: - Spontaneous recovery is expected within 3–6 months - Surgery is reserved for **chronic, non-recovering palsies** (>6–12 months) - Premature surgery risks overcorrection if recovery occurs later