I have a few patients whom I thought had an atypical form of wet AMD, but the retinal specialist treated them with intravitreal anti-VEGF to no avail. Is there something else I should be looking for?
A: The anti-VEGF revolution has allowed us to inhibit AMD progression and in some cases actually recover visual function, according to Jay Haynie, OD, of Retina and Macula Specialists in Tacoma, WA. “However, some patients fail to respond to this staple treatment modality.” Given the standard-bearing nature of anti-VEGF, a lack of response is enough to raise eyebrows. “Several reasons exist as to why; however, one thing to be critical of is whether you have the correct diagnosis,” says Dr. Haynie.
|Fluorescein angiogram reveals late leakage in the temporal fovea of the right eye. Note the “right angle” appearance of the vasculature. Click image to enlarge.|
Macular telangiectasia (MT) often presents with visual symptoms and retinal findings resembling AMD, leading to misdiagnosis. “Patients with MT tend to have similar visual symptoms as sufferers of AMD: distortion, missing letters and trouble reading fine print,” says Dr. Haynie. The symptoms of MT also tend to develop in the fourth to sixth decades of life, similar to AMD, he adds.
OCT Reveals the Culprit
While AMD and macular telangiectasia present with similar clinical findings, they show quite differently on OCT, revealing the disparate nature of each condition. Indeed, the etiopathogeneses of the two conditions do not overlap, and this is reflected in their differential responses to anti-VEGF treatment. Careful examination of the OCT—in particular, looking at the RPE complex and inner retinal layers—can reveal the culprit, says Dr. Haynie. “AMD is a disease of the choroid and ultimately alters the contour of the RPE while sparing the inner retinal layers. In contrast, macular telangiectasia initially causes an alteration of the inner retina. In the late phases it disrupts the outer retinal layers; however, the RPE layer remains intact in most cases,” he says.
On SD-OCT, Dr. Haynie says one can differentiate AMD from MT easily if you understand the diseases. “In MT, you will initially see inner retinal changes that are described as ‘schisis-like’ changes as opposed to cystoid spaces, per se,” he says. As the condition progresses—over decades for most—the outer retina begins to thin along with an alteration of the ellipsoid and PIL structures seen on the OCT, he explains.
Clues in the Fundus
Fundus findings in both conditions also have their share of similarities and key differences. “Macular telangiectasia is not associated with hallmarks of AMD (i.e., drusen and subretinal hemorrhage). However, they both show macular pigment mottling and, given the ages of the patients—generally the fourth to sixth decade of life—the diagnosis of AMD is made,” says Dr. Haynie. Yet, there are findings to look out for in the fundus in order to differentiate the two conditions. “In the posterior segment, the retinal surface appears crystal-like in appearance; the parafoveal area appears gray and thick and small, irregular capillaries can be seen, generally temporal to the fovea,” says Dr. Haynie. “These telangiectatic vessels are best seen with red-free photography or fluorescein angiography and are pathognomonic for the disease,” he explains. Importantly, Dr. Haynie says that the clinical fundus characteristics in MT vary from that of AMD in that no drusen hemorrhage or lipid is seen upon your clinical examination.
MT is not well understood. “Unless the disease has progressed to the fifth stage—characterized by the development of CNV and subretinal fibrosis—it does not respond to anti-VEGF compounds.” And in Dr. Haynie’s experience, very few cases progress to stage five over patients’ lifetimes. So, keep in mind that a lack of response to VEGF blockade may be a signal of a disease not associated with AMD, such as macular telangiectasia.