IgG4-related orbital or ophthalmic disease is a manifestation of systemic IgG4-related disease that accounts for a substantial minority of what was previously considered idiopathic orbital inflammation (orbital pseudotumor).
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Clinical presentation
Patients usually present with either painless periorbital/eyelid swelling or proptosis, with or without diplopia 1-3. Pain affects a small fraction 3.
Pathology
Location
Within the orbit, IgG4-related disease can involve one or multiple tissue compartments, including the lacrimal gland (dacryoadenitis), extraocular muscles (orbital myositis), orbital fat, sclera, and cranial nerve branches. The most common sites are the lacrimal gland and extraocular muscles, which are affected in the majority of patients with this diagnosis 1-3.
Immunophenotype
Orbital IgG4-related disease requires immunohistochemistry demonstrating at least 30 IgG4-positive plasma cells per high power field 4.
Radiographic features
On CT and MRI, the primary imaging features are enlargement of the lacrimal gland and/or extraocular muscle(s) 3. Involvement is bilateral in a majority 1,3. The muscle most often affected and most prominently enlarged is the lateral rectus muscle 3. The anterior tendon is spared in the vast majority 3.
Supportive features present in a minority of cases include inflammation in the orbital fat, infraorbital nerve enlargement, and paranasal sinus disease 3.
Differential diagnosis
The entity overlaps with other infiltrative disorders of the orbit.
thyroid-associated orbitopathy commonly causes tendon-sparing extraocular muscle enlargement, but it does not involve the lateral rectus until late in the disease and does not involve the infraorbital nerve 3,5
idiopathic orbital inflammation can also cause extraocular muscle enlargement, but it usually involves the anterior tendon, is more commonly unilateral, and more often affects the medial rectus than lateral rectus 3
See these separate articles for a full differential: