Article Date: 6/1/2007

A Pattern Dystrophy of The Retinal Pigment Epithelium
CASE STUDY:

A Pattern Dystrophy of The Retinal Pigment Epithelium

The late-onset of macular conditions in this man lead to a misdiagnosis of age-related macular degeneration.

DIANA L. SHECHTMAN, O.D., F.A.A.O., Fort Lauderdale, Fla. & DIANE E. CALDERON, O.D., F.A.A.O., Fort Lauderdale, Fla.

A 73 year-old black man presented to our clinic for a second opinion of a recent diagnosis of age-related macular degeneration (AMD) O.U. He reported no ocular or visual complaints. His past ocular history revealed no other abnormalities, and his past medical and family histories were both unremarkable.

Exam findings

The patient's best-corrected visual acuity was 20/25 O.U. Both pupils were equal, round and reactive to light with no afferent pupillary defect. Amsler grid revealed no central scotomas or metamorphopsias O.U. Slit lamp evaluation was only remarkable for mild nuclear sclerosis O.U. Dilated fundus exam showed symmetrical sub-retinal oval lesions in the macula with surrounding drusen-like deposits (see figures 1a and 1b).

Figure 1a & 1b: Symmetrical sub-retinal oval lesions in the macula with surrounding drusen-like deposits.

To further evaluate these lesions, we performed an optical coherence tomography (OCT) scan (see "The OCT and Pattern Dystrophies," page 72). The OCT revealed bilateral hyper-reflective, domeshaped elevations within the retinal-pigment epithelium (RPE), just below the fovea (see figure 2). We didn't observe any associated subretinal or intraretinal fluid, which may accompany such findings. The retinal map revealed a normal central retinal thickness of 191μm O.U. Retinal thickness was not affected since the lesion was isolated to the RPE and there was no associated retinal edema.

Figure 2: OCT shows hyper-reflective, dome-shaped elevations within the retinal-pigment epithelium (RPE).

Diagnosis

We diagnosed this patient with a retinal pattern dystrophy of the RPE — adult-onset foveomacular vitelliform dystrophy (AFVD). The solitary, "egg-yolk" pigmented lesion seen in this patient is a typical sign of this retinal pattern dystrophy of the RPE (see figures 1a and 1b).

Discussion

Researchers first described pattern dystrophies of the RPE (a group of disorders) in 1977.1 Pattern dystrophies are characterized by diverse pigmented or yellow configurations within the macula. These deposits are classically bilateral and symmetrical. The classifications of pattern dystrophies are primarily based upon the deposit distribution within the RPE.2

Aside from AFVD, this group of disorders includes butterfly-shaped pigmented dystrophy, reticular dystrophy and fundus pulverulentus.2 Patients with pattern dystrophies may show distinct configurations between the eyes. Researchers have described that pattern dystrophies can even transform from one pattern type to another.

AFVD is similar to Best's disease, characterized by a small round subfoveal "egg-yolk" lesion. Unlike AFVD, Best's disease patients typically manifest signs of the condition by age 10.2 Practitioners commonly observe AFVD in early adulthood with signs and symptoms manifesting in the third and fifth decade of life.2 The clinical presentation of Best's disease generally includes a larger lesion, progressive disruption of the lesion and abnormal electro-oculogram (EOG), all of which differentiates it from AFVD.

The OCT and Pattern Dystrophies
The ability of the OCT to depict a cross-sectional image of the retina allows you to distinguish overlying and underlying retinal pathology. You can also visualize subtle changes, such as disruption and/or atrophy of the RPE/sensory retina, through the use of OCT imaging. OCT is particularly useful in monitoring progression, since you can take a quantitative and qualitative measurement of associated retinal thickness and pattern size.8
You may observe retinal edema in the OCT of both wet-AMD and a pattern dystrophy of the RPE. Yet, the classic presentation of wet-AMD is characterized by a CNV lesion depicted in the OCT as a fusiform hyper-reflective area above or below the RPE.
OCT imaging of pattern dystrophies are as variable as the fundoscopic appearances. The typical finding includes a thickened hyper-reflective lesion within the RPE. Researchers believe these deposits are an abnormal accumulation of lipofuscin — a waste by-product in the RPE linked to free-radical damage.2
Auxiliary testing, such as OCT, is not only valuable in helping determine the diagnosis, but it also aids in the identification of subtle fundoscopic-associated findings, such as subretinal thickening, retinal serous detachment and CNV.9 It is critical to properly diagnose these conditions, so we can manage them appropriately.

Butterfly-shaped dystrophy has a tri-radiation pattern of yellow or darkly pigmented deposits. Reticular dystrophy has granular "fishnet" deposits, radiating out and extending into the mid-periphery. Pulverulentus dystrophy, the rarest of these conditions, has an early, spotty, mottled pigmentation in the posterior pole that eventually develops into a coarse "punctiform," mottled RPE.

Patients with any pattern dystrophy of the RPE may present with drusen-like deposits and pigmentary changes. Choroidal neovascularization (CNV), although rare, can be associated with these dystrophies.3

Because of the late onset of these macular conditions, practitioners often misdiagnose pattern dystrophies as AMD. Patient demographics, aspects of the clinical presentation and auxiliary testing, such as OCT, may help determine the correct diagnosis.

The inherited mode of these conditions is autosomal dominant, with associated mutations localized to the peripherin/retinal degeneration slow (RDS) gene.4-7 Due to the variability in expression and gene penetration, manifestations of these diseases are inconsistent, with variable presentations within family or even the same individual. While practitioners most often observe the actual macular changes in the second to fifth decade of the patient's life, the visual disturbances aren't significant.4 Typical symptoms include decreased acuity and metamorphopsia.4,5

Management

We educated our patient on his condition and recommended he return to us on a bi-annual basis so we could monitor his AFVD for progression or complications. Complications associated with progression of these subretinal lesions may include associated retinal edema and, although rare, CNV.

We also suggested that his family members be evaluated with a comprehensive eye exam, including dilation, due to the inherited nature of the disease. Finally, we provided him with a home Amsler grid to monitor any visual changes.

The prognosis for pattern dystrophies is good, with patients maintaining reading-level vision in at least one eye throughout the remainder of their life.3

This patient has not yet returned to the clinic. OM

References available upon request.

Dr. Shechtman is an associate professor at Nova Southeastern University College of Optometry in Ft. Lauderdale and works at the eye institute and diabetic/macula clinic. She is a member of the optometric retinal society (ORS). E-mail her at dianashe@nova.edu.
Dr. Calderon is an assistant professor at Nova Southeastern University College of Optometry, and she is an attending practitioner in the primary care clinics. E-mail her at dcaldero@nova.edu.


Optometric Management, Issue: June 2007