Idiopathic Orbital Inflammation

A non-infective inflammatory condition of the orbit without an identifiable local or systemic cause, previously termed orbital pseudotumour. It is a diagnosis of exclusion.

• Pattern by site: myositis (extraocular muscle, including tendon), dacryoadenitis, anterior (scleritis, tenonitis), diffuse, apical (orbital apex syndrome), sclerosing (fibrosis dominant, steroid resistant), and perineuritis.
• Most are unilateral in adults aged 30 to 60; childhood cases (about 6 to 17 percent) are often bilateral, with eosinophilia, uveitis and systemic features.
• Mimics: IgG4-related disease, granulomatosis with polyangiitis, sarcoidosis, lymphoma, thyroid eye disease, infection, metastasis, vasculitis, giant cell arteritis, Erdheim-Chester disease, Rosai-Dorfman disease, and Langerhans cell histiocytosis.

• Acute onset (days) of orbital pain (often severe, worse on eye movement), periorbital erythema and swelling, proptosis, chemosis, diplopia and restricted movement.
• Myositis: pain on gaze toward the muscle, injection over the muscle insertion, restricted movement in the field of the muscle; thick tendon on imaging (differentiates from thyroid eye disease, which spares the tendon).
• Dacryoadenitis: swelling of the lateral upper lid with S-shaped ptosis and tender gland.
• Apical: reduced vision and ophthalmoplegia with little proptosis.
• Sclerosing: chronic painless progressive course with fixed globe.
• Reduced acuity, relative afferent pupillary defect, disc swelling, or choroidal folds indicate compressive or inflammatory optic neuropathy.

• Orbital MRI with fat suppression and gadolinium (diffuse enhancement) or CT (muscle enlargement with tendon involvement, ill defined soft tissue, lacrimal gland enlargement, no bone destruction).
• Blood tests: full count (eosinophilia), ESR, CRP, ANA, rheumatoid factor, ANCA, ACE, IgG subclass (IgG4 above 135 mg/dL supportive), thyroid function and antibodies, syphilis serology, hepatitis, tuberculosis test, blood cultures; chest imaging.
• Biopsy when there is atypical presentation, no response to steroids within 1 to 2 weeks, bilateral or recurrent disease, apical or sclerosing disease, mass like lesion, or age under 18 or over 60. Typical myositis can be treated without biopsy.
• Histology: polymorphous lymphoid infiltrate with fibrosis; exclude lymphoma (immunohistochemistry and clonality) and IgG4 plasma cells.

• Oral prednisolone 1 to 1.5 mg/kg daily (60 to 80 mg) for 1 to 2 weeks, then taper over 6 to 12 weeks guided by response. Rapid improvement within 24 to 72 hours supports the diagnosis. Provide gastric and bone protection, check glucose and blood pressure.
• Sight threatening disease: methylprednisolone 500 mg to 1 g IV daily for 3 days, then oral steroid.
• Relapses (about 50 percent, more in myositis and sclerosing types): steroid sparing agents, in order of use: methotrexate 15 to 25 mg weekly with folic acid 5 mg weekly, azathioprine 2 to 2.5 mg/kg daily, mycophenolate mofetil 1 g twice daily, rituximab 1 g IV on days 1 and 15 (or 375 mg/m2 weekly for 4 doses), tocilizumab 8 mg/kg IV monthly, or infliximab.
• Orbital radiotherapy (20 to 30 Gy in 10 to 15 fractions) for refractory disease unresponsive to drugs or when steroids contraindicated.
• Local steroid injection (triamcinolone 20 to 40 mg) for dacryoadenitis and anterior disease selected cases.
• Non-steroidal anti-inflammatory drugs for mild myositis; follow up every 2 to 4 weeks during taper.
• Debulking surgery rarely, and decompression for compressive neuropathy.