Congenital hypertrophy of the retinal pigment epithelium (CHRPE)

Description

Congenital hypertrophy of the retinal pigment epithelium or RPE (ChlRPE or ‘chirpy’) is a benign condition where the pigmentary lesions may be unilateral or bilateral, solitary or multifocal, with the latter sometimes being in the form of smaller patches that are grouped together, giving the impression of animal paw prints (bear tracks) in the fundus. Lesions of an atypical appearance may be a marker for familial adenomatous polyposis (FAP), most commonly in Gardener syndrome, an autosomal dominant condition in which essentially all patients will develop colorectal carcinoma without prophylactic proctocolectomy. In CHRPE, the RPE cells are larger and contain more melanin granules than normal. Adenocarcinoma developing from CHRPE has been reported but is considered a rare occurrence.

Symptoms

There are no symptoms associated with CHRPE.

Signs

A typical CHRPE is flat and black or grey, with a sharply defined border, contrasting with the slate-grey, ill-defined appearance of a choroidal nevus. They can range from very small to many disc diameters in size. Frequently, a depigmented halo lies just inside the edge of the lesion. Further depigmented areas or lacunae may develop within the lesion with time. This is sometimes referred to as a sunburst effect. Some CHRPEs are conspicuously lacking in pigment, just having a pigmented edge. The multifocal, so-called bear-track form of CHRPE is often confined to a specific area within the fundus. CHRPEs that are associated with FAP are described as atypical, being oval or even fishtail like in shape, bilateral, more isolated in position rather than grouped together and variable in size up to approximately a disc diameter. CHRPEs block choroidal fluorescence on fluorescein angiography.

Prevalence

Multifocal CHRPE are fairly common and occur in about 1% of the population. Solitary lesions in one eye are less common. CHRPE associated with FAP are rare and are seen in about 1 in 100,000 people.

Differential diagnosis

Other pigmented lesions of the fundi include: melanoma – choroidal, choroidal nevus; combined hamartoma of the RPE; choroidal metastases from malignant melanoma elsewhere in the body; retinal adenocarcinoma; chorioretinal scarring
(RPE hyperplasia).

Management

Imaging Routine examination and serial photography are all that is usually required.

Advice There is no treatment for CHRPE. The possibility of adenocarcinoma arising from a CHRPE is rare. The practitioner should keep in mind the potential systemic association with FAP, albeit uncommon, and refer patients with suspicious lesions or a suggestive case history to their general practitioner for evaluation. Single lesions in one eye, or those forming grouped pigmentation, are not considered to be associated with FAP.