Orbital lesions comprise a wide spectrum of tumors and pseudotumors whose origin can be inflammatory, infectious, hemorrhagic or neoplastic. Regardless of the etiology, these lesions can adopt similar presentations including a palpable mass, eyelid swelling, ptosis, erythema, restricted eye motility, diplopia, periocular pain and vision loss. Correct diagnosis is essential given that the unnecessary removal of the masses can damage intraorbital structures, while some malignant tumors must be excised. The most frequent malignant orbital tumor in adults is a B-cell non-Hodgkin lymphoma that arises from mucosa-associated lymphoid tissue (MALT). It usually presents as a painless slowly progressive growing mass; a biopsy being required for diagnostic confirmation but complete excision not being indicated unless it is small and localized. Idiopathic orbital inflammation (IOI) is another frequent orbital disease that can mimic an orbital tumor. It is a benign non-specific inflammatory syndrome of the orbit without identifiable causes whose typical clinical features include pain, proptosis and inflammatory signs and symptoms. Corticosteroids remain the first-line treatment in most cases. IgG4-related disease (IgG4-RD) is a systemic autoimmune inflammatory process characterized by tissue infiltration by IgG4-bearing plasma cells. It has been reported in almost every organ, but orbital structures are frequently involved. IgG4-related orbital disease (IgG4-ROD) presents with painless eyelid swelling, proptosis and diplopia as common symptoms. Histopathological examination is the current gold standard for the diagnosis and the initial treatment approach are systemic glucocorticoids.

We present a case of a 52-year-old man with ophthalmoparesis and bilateral orbital mass as the presenting features of a IgG4-RD, which presented a diagnostic challenge.