Familial Adenomatous Polyposis

This patient was first seen for a routine eye exam at 7 years of age. VA was 20/20 and anterior examination was normal in each eye; however, a dilated eye exam revealed multiple bilateral pigmented retinal lesions (four OD and six OS).

THE DIAGNOSIS

The hallmark pathologic finding of familial adenomatous polyposis (FAP) is the development of hundreds to thousands of polyps in the colon and rectum by the second decade of life. These polyps eventually transform into colorectal cancer (7% risk by age 21, increasing to 87% by age 45 and 93% by age 50).^1-3 When associated with extracolonic lesions, such as pigmented retinal lesions, desmoid tumors, osteomas, dental anomalies, or sebaceous or epidermoid cysts, the condition is known as Gardner syndrome,^1,4 as first described in 1952 by Eldon J. Gardner and Ralph C. Richards.¹ Early diagnosis and appropriate treatment is essential for patients with this condition.

FAP is caused by mutations in the adenomatous polyposis coli gene, which is a tumor-suppressing gene located on chromosome 5.¹ This mutation does not trigger cancer, but instead reduces the body’s ability to prevent cells from becoming cancerous. FAP is autosomal dominant and, as such, half of the children of an affected parent will develop FAP.^1,4 However, de novo mutations (new mutations with no family history) account for 20% to 30% of cases.⁵

Pigmented fundus lesions are the most common and earliest extracolonic manifestations of FAP.² These benign retinal lesions are found in 50% to 90% of patients with FAP and are often present at birth.^1-7 Lesions are atypical, multiple, bilateral congenital hypertrophy of the retinal pigment epithelium (CHRPE) with a round or oval shape and a “fishtail” hypopigmented area at one or both ends.⁵ These lesions are asymptomatic and have little visual significance other than to prompt further evaluation for FAP.

The differential of these pigmented lesions includes solitary and grouped CHRPE, or “bear tracks.”⁵ These RPE lesions are histologically different from FAP retinal lesions and have a distinct clinical appearance, demonstrated in the Figure. Specifically, FAP retinal lesions tend to be oval with a marginal gray or depigmented halo.⁶

NEXT STEPS

The patient was referred for genetic testing and gastrointestinal evaluation. He tested positive for FAP, although both parents were negative. The patient is now 11 years of age and has had yearly colonoscopies with multiple colon polyps removed every year, including one duodenal polyp. He has also had an epidermal cyst removed from his scalp.

Initially, when this patient’s optometrist informed his parents that their 7-year-old boy may be at risk for colon cancer, they were skeptical, to say the least. With no family history of colon cancer, it took some convincing for them to follow through with genetic testing.

Trust your gut when you see atypical CHRPE lesions. Taking the extra step to get your patients the proper referral could save their lives.