Atypical optic neuritis challenging to diagnose

Newark, NJ-Atypical optic neuritis raises red flags for ophthalmologists that can help differentiate it from typical optic neuritis.

"When a patient presents with atypical optic neuritis, there are points in the history and the examination that are red flags, including bilateral optic neuritis, progression beyond 1 week, recurrence within a short period, the presence of an acute systemic illness at onset, or a systemic illness that is known to be associated with optic neuritis," said Larry Frohman, MD. "Red flags present on examination include Argyll-Robertson pupils, proptosis, lacrimal gland abnormalities, uveitis, ophthalmoplegia, and trigeminal-nerve involvement."

Other clues that the optic neuritis may be atypical are the presence of neurologic signs that are not consistent with multiple sclerosis and retinal disease such as periphlebitis, granuloma, macular scars, or retinovascular disease, explained Dr. Frohman, associate professor of ophthalmology and visual sciences and neurology and neurosciences, University of Medicine and Dentistry-New Jersey Medical School, Newark, NJ.

Among the retinal diseases, acute big blind spot syndrome, acute macular neuroretinitis, and cone dystrophy may mimic optic neuritis, he explained.

With the last, characterized by color vision loss and central scotoma, electrophysiologic testing may have to be performed to establish the diagnosis. Dr. Frohman advised that photopsia or metamorphopsia may be clues to the presence of retinal disease. Optical coherence tomography is emerging as a tool in the identification of subtle maculopathies.

Compressive optic neuropathy can mimic optic neuritis, but this is rarely the case, according to Dr. Frohman. Infiltration of the meninges by carcinoma cells can also mimic optic neuritis.

"In both of these, the progressive clinical course is a red flag that this is not typical optic neuritis," he emphasized.

Likewise, in most cases toxic optic neuropathy has a chronic indolent course. This optic neuropathy is bilateral and symmetric, which differs from typical disease.

"Leber's optic neuropathy may be difficult to differentiate from typical optic neuritis in the absence of a family history of Leber's optic neuropathy. In some cases, when seen acutely, the disc may have telangiectasia," Dr. Frohman explained.

Systemic infectionsCertain systemic infections such as syphilis, Lyme disease, cat-scratch disease, tuberculosis, or post-viral optic neuritis can mimic the appearance of typical optic neuritis. In syphilis, the appearance of the disc can range from normal to markedly swollen and neuroretinitis can be seen, he pointed out. Interstitial keratitis, scleritis, uveitis, and chorioretinitis are other clues that syphilis may be present.

Lyme disease has seldom been reported to cause optic neuritis as well as optic perineuritis, neuroretinitis, and a clinical picture that resembles pseudotumor cerebri. Signs and symptoms of Lyme disease include conjunctivitis, keratitis, uveitis, and vitritis, as well as systemic symptoms.

While cat-scratch disease also mimics optic neuritis, fortunately, according to Dr. Frohman, its fundus appearance is specific to itself and is not seen in typical optic neuritis. The disc usually looks swollen with a full, hemi, or partial macular star. Gram-negative Bartonella henselae is the offending organism that results in fever, malaise, and lymphadenopathy.

"Tuberculosis is always included in the differential diagnosis of atypical optic neuritis but is rarely seen in the United States," Dr. Frohman explained. "Disc involvement varies in tuberculosis, and clues include granulomas, uveitis, vitritis, choroiditis, and dacryoadenitis."

In post-viral optic neuritis, history is the key: it usually occurs 1 to 3 weeks after a systemic illness, is bilateral, and commonly occurs in children. The swelling of the disc varies and may be similar to that seen after vaccination.

Sarcoidosis, systemic lupus erythematosus (SLE), and vasculitis can mimic typical optic neuritis. Sarcoid optic neuropathy may be "grossly underdiagnosed," according to Dr. Frohman, and can be the presenting sign of occult sarcoid.