A 32-year-old woman presents with sudden-onset floaters, photopsia, and blurred vision in the right eye for 3 days. Examination reveals vitritis with 3+ haze, posterior synechiae, and a granulomatous anterior chamber reaction. Fundus examination shows multiple cream-coloured nodules at the macula and optic disc. Which investigation is most appropriate to establish the aetiology of this posterior uveitis?

Explanation

## Clinical Presentation Analysis This patient presents with **granulomatous uveitis** (granulomatous anterior chamber reaction, posterior synechiae) with **multifocal choroidal infiltrates** (cream-coloured nodules at macula and optic disc). This constellation is highly suggestive of **sarcoidosis**. ## Why Chest X-ray and Serum ACE? **Key Point:** Sarcoidosis is a systemic granulomatous disease affecting the lungs in >90% of cases. Ocular involvement is the presenting feature in 10–15% of sarcoidosis patients. **High-Yield:** The diagnostic workup for suspected sarcoidosis-related uveitis includes: 1. **Chest X-ray** — identifies hilar lymphadenopathy, parenchymal infiltrates (Löfgren syndrome = acute triad: hilar LN + erythema nodosum + arthritis) 2. **Serum ACE (angiotensin-converting enzyme)** — elevated in ~60% of sarcoidosis patients; supports systemic diagnosis 3. **Serum calcium** — hypercalcaemia in 10% (granuloma-mediated calcitriol production) **Clinical Pearl:** Multifocal choroidal infiltrates ("candle-wax" or cream-coloured nodules) are pathognomonic for sarcoidosis-related posterior uveitis and are rarely seen in tuberculosis or other infectious causes. ## Differential Investigations | Investigation | Indication | When to Use | |---|---|---| | Chest X-ray + ACE | Sarcoidosis (systemic granulomatous disease) | **First-line for granulomatous uveitis with multifocal choroidal involvement** | | Vitreous biopsy + PCR TB | Infectious uveitis (TB, CMV, ARN) | Reserved for diagnostic uncertainty, immunocompromised, or treatment failure | | AC paracentesis + culture | Bacterial anterior uveitis | Not indicated in granulomatous disease; culture yield low | | FFA alone | Characterizes vascular leakage, ischaemia | Diagnostic tool, not aetiological; must follow systemic workup | **Mnemonic: SARCOID causes Granulomatous Uveitis — Systemic Assessment Required (Chest X-ray, ACE, Calcium) before Ocular Investigation Done** [cite:Park 26e Ch 12]