A 28-year-old man from rural Maharashtra presents with progressive night blindness for the past 3 years, followed by gradual constriction of his visual fields. On examination, visual acuity is 6/9 in both eyes. Fundoscopy reveals bone spicule-like pigmentation in the mid-periphery of the retina, attenuated retinal vessels, and a pale optic disc. Electroretinography (ERG) shows reduced amplitudes with relatively preserved central responses. The patient's father had similar symptoms starting in his 20s. What is the most likely diagnosis?

Explanation

## Diagnosis: Retinitis Pigmentosa ### Clinical Presentation This patient exhibits the classic triad of retinitis pigmentosa (RP): 1. **Night blindness (nyctalopia)** — earliest symptom, due to progressive loss of rod photoreceptors 2. **Progressive visual field constriction** — concentric visual field loss, starting peripherally 3. **Bone spicule pigmentation** — pathognomonic retinal finding in mid-periphery ### Fundoscopic Findings | Feature | Retinitis Pigmentosa | |---------|---------------------| | Pigmentation pattern | Bone spicule-like, mid-peripheral | | Retinal vessels | Attenuated (narrow) | | Optic disc | Pale, waxy appearance | | Macula | Initially spared (late involvement) | ### Electroretinography (ERG) **Key Point:** ERG is the gold standard for diagnosis. In RP, both rod and cone responses are reduced, but rod dysfunction is disproportionately severe and occurs earlier. The pattern of reduced amplitudes with relatively preserved central (macular) responses is characteristic. ### Inheritance Pattern **High-Yield:** RP shows three inheritance patterns: - **Autosomal recessive** (most common, ~50%) - **Autosomal dominant** (~30%) - **X-linked** (~20%, more severe) This patient's father was affected, suggesting **autosomal dominant inheritance** (though autosomal recessive with consanguinity is also possible in India). ### Pathophysiology **Mnemonic:** RP = **Rod-Cone degeneration Progressive** - Rods affected first and most severely → night blindness - Cones affected later → central vision loss and colour vision defects - Photoreceptor loss → secondary retinal pigment epithelium (RPE) migration → bone spicule appearance ### Natural History 1. **Early phase (teens–20s):** Night blindness, peripheral field loss 2. **Middle phase (20s–40s):** Progressive field constriction, reduced central vision 3. **Late phase (40s+):** Central vision loss, potential legal blindness **Clinical Pearl:** Macular involvement is a late feature; early preservation of central acuity (6/9 here) is typical and distinguishes RP from conditions with primary macular pathology. ### Associated Systemic Findings - **Kearns-Sayre syndrome:** RP + cardiac conduction defects + cerebellar ataxia (mitochondrial inheritance) - **Refsum disease:** RP + peripheral neuropathy + ataxia + cardiomyopathy (treatable with dietary management) - **Bassen-Kornzweig syndrome:** RP + fat malabsorption + neurological signs (vitamin E deficiency) This patient has isolated ocular findings with family history, consistent with non-syndromic RP.