Pigmentosa

Sunir J. Garg


BASICS


DESCRIPTION


• Group of hereditary, progressive retinal diseases that result in the degeneration of rod (mainly) and cone photoreceptors; the degeneration starts in the mid-periphery and advances toward the macula.


• Significant phenotypic and genotypic diversity


EPIDEMIOLOGY


Incidence


• N/A


Prevalence


• 1 in 3,000—5,000 persons


RISK FACTORS


• None


Genetics


• 60% of affected people have associated genetic mutations


• Inherited forms could be autosomal dominant (30–40%), autosomal recessive (50–60%), or X-linked (5–15%).


• Even with the same genotype, patients can present with different manifestations.


• In non-syndromic retinitis pigmentosa (RP), more than 45 genes/loci have been isolated


• Most common genes (30% of RP cases):


– Rhodopsin gene (RHO): 25% of autosomal dominant RP


– USH2A gene: 20% of recessive disease


– RPGR gene: 70% of X-linked RP


GENERAL PREVENTION


• Controversial: Use of dark glasses to slow progression of retinal damage.


PATHOPHYSIOLOGY


• Primary degeneration of rod photoreceptors, and secondary degeneration of cone photoreceptors.


• The exact mechanism has not been established.


ETIOLOGY


• Genetic inheritance in 60%


COMMONLY ASSOCIATED CONDITIONS


• 20–35% of cases are associated with non-ocular disease (about 30 syndromes)


• Usher’s Syndrome (10–20% of RP cases): Congenital or early deafness followed by RP in teenage years


• Bardet-Biedel syndrome (5% of RP cases): RP, obesity present in childhood, renal failure, hypogonadism, polydactyly, mental retardation, or mild psychomotor delay.


DIAGNOSIS


HISTORY


• Variable; some have symptoms starting in childhood, while others have symptom onset during young adulthood.


• Nyctalopia (night blindness) is the most common symptom and presents earlier in autosomal recessive form; median age of onset 24 years.


• Constricted mid-peripheral visual fields in early adulthood, which leads to tunnel vision in advanced cases.


• Although many patients have good central acuity for decades, a number eventually develop significant vision loss.


• Photophobia, especially in diffuse light (e.g., overcast days) – difficulty with reading, due to the narrow window between too much and insufficient light.


• Photopsia (35%) – late sign


PHYSICAL EXAM


• Anterior segment


– Posterior subcapsular cataract (50%)


• Posterior segment


– Waxy pallor of the optic nerve head


– Attenuated retinal vessels


– Retinal hypo- and hyper-granularity


– Bone spicule formation around intraretinal vessels (mid to far periphery)


– Cystoid macular edema


– Optic nerve head drusen (10%)


– Vitreous cells


• Sectoral RP: Variant of RP; only 1 or 2 quadrants are affected


• Color vision testing can be normal, or show blue cone dysfunction in advanced RP (acquired tritanopia)


• Decreased contrast sensitivity (Pelli-Robson chart)


DIAGNOSTIC TESTS & INTERPRETATION


Lab


Initial lab tests

• Genetic tests, if available


Follow-up & special considerations

• N/A


Imaging


Initial approach

• Optical coherence tomography (OCT) is useful to measure retina thickness, assess the photoreceptor layer, and to assess the presence and degree of cystoid macular edema.


Follow-up & special considerations

• OCT imaging in subsequent follow-ups.


Diagnostic Procedures/Other


• Electroretinogram (ERG) is critical to confirm the diagnosis and assess degree of visual impairment: Diminuted a- and b-wave amplitude and delayed timing during scotopic and photopic conditions are seen even in early stages.


• Visual field tesing initially shows patchy loss of peripheral vision; progresses to mid-peripheral field loss; in advanced cases, only far peripheral and central island of vision remains (“tunnel vision”). Goldmann (kinetic) perimetry is more useful to assess peripheral vision changes.


Pathological Findings


• Rod and cone degeneration


• Bone spicule pattern is due to hyperplasia and migration of RPE cells into the neurosensory retina in response to photoreceptor cell loss.


• Waxy pallor of the nerve: Indicates axonal loss and overlying gliosis


DIFFERENTIAL DIAGNOSIS


• Leber congenital amaurosis – when visual loss is present from birth or first 5 years of life.


• Cancer/melanoma associated retinopathy


• Congenital stationary night blindness


• Fundus albipunctatus


• Vitamin A deficiency


• Congenital infections: Rubella, syphilis


• X-linked disorders: Choroideremia, ocular albinism


• Mitochondrial disease: Kearns-Sayre syndrome


• Gyrate atrophy


• Retinoschisis


• Hereditary vitreoretinopathies: Familial exudative vitreoretinopathy, Wagner disease, Stickler syndrome


• Inflammatory disorders: Birdshot choroidoretinopathy, serpiginous retinopathy, multifocal placoid pigment epitheliopathy, sarcoidosis


• Maculopathies: Stargardt disease, Cone dystrophies, Sorsby disease


TREATMENT


MEDICATION


First Line


• Vitamin A Palmitate 15,000 units daily


• Omega 3 fatty acids (1400 mg daily)


• Lutein 12 mg daily



ALERT


• If prescribing high dose Vitamin A, need to monitor serum levels for retinol, triglyceridemia, and liver enzymes.

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Nov 9, 2016 | Posted by in OPHTHALMOLOGY | Comments Off on Pigmentosa
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