What is Nonspecific Orbital Inflammation (NSOI)?

Nonspecific orbital inflammation (NSOI), also known as psuedotumor, is disease of the eye that not uncommonly presents to the emergency room or ophthalmologist. Typically, its onset is acute and manifests with severe orbital pain, swelling around the eyes, limitation and pain with eye movements, and even loss of vision. It is easily confused with infection (pre-septal or post-septal eyelid cellulitis) and may be treated initially –and unsuccessfully– with antibiotics.

Computed tomography of the orbits may reveal thickening of the extraocular muscles, stranding of the orbital fat, a poorly defined mass (hence the name “pseudotumor”), thickening of the sclera, soft tissue inflammation in the eyelids, or even nothing at all. NSOI can affect children as well as adults. Typically, it responds very quickly to high dose corticosteroids. In fact, this rapid response usually confirms the diagnosis. Atypical presentations warrant further testing, including blood tests and tissue biopsy.

NSOI is so named because of the way a biopsy of affected tissue appears microscopically. There is a scattering of plasma cells, lymphocytes, neutrophils, and histiocytes with no particular pattern. The differential diagnosis for pseudotumor includes the following: thyroid-associated orbitopathy (Graves’ disease), non-infectious granulomatous inflammation (specific orbital inflammation such as Wegener’s granulomatosis and sarcoidosis), infectious orbital inflammation (bacterial, fungal, and parasitic), lymphocytic inflammation (Sjogren’s syndrome and Kimura’s disease), xanthogranulomatous and histiocytic inflammations (non-Langerhans cell histiocytosis and Langerhans cell histiocytosis), fibrotic inflammation (idiopathic sclerosing orbital inflammation and chronic dacryocystitis), and amyloid deposition.

The treatment for NSOI is immunosuppression. Typically, high dose oral prednisone at 60-80 mg a day is tapered over a long period of months. Occasionally, patients may become steroid dependent and unable to be weaned from the prednisone without relapses. Alternative treatments include other forms of immunosuppression, such as methotrexate and immunomodulators such as infliximab. Irradiation of the orbit is also an option, although a tissue diagnosis should be obtained before pursuing radiation treatment. Irradiation is contraindicated in patients with diabetes, due to potential worsening of diabetic retinopathy.