IgG4-ROD is a recognized manifestation of IgG4-RD and may be the first or only clinically apparent site of disease. Although lacrimal gland enlargement is a classic pattern, involvement may extend to orbital fat, extraocular muscles, eyelids, the orbital apex, and trigeminal nerve branches [2-5]. Recent series confirm a broad spectrum of unilateral and bilateral presentations, with proptosis, eyelid swelling, ptosis, and motility restriction among the most common symptoms [2,4,5]. The present patient had a unilateral superolateral orbital mass with ptosis and impaired elevation, but no diplopia or reported visual loss.

The radiological distinction between IgG4-ROD and orbital lymphoma may be difficult. Both conditions can produce a homogeneous soft-tissue mass, lacrimal-region enlargement, extraocular muscle involvement, or diffuse orbital infiltration. Bilaterality, enlargement of infraorbital or supraorbital nerves, and multisite ocular adnexal involvement may support IgG4-ROD, but none is sufficiently specific to replace biopsy [2,3]. In this case, the unilateral intraconal and extraconal lesion was interpreted as possibly lymphomatous, an appropriate concern given the patient's age and the progressive mass effect.

Histopathology remains central to diagnosis. The characteristic morphological triad of systemic IgG4-RD consists of a dense lymphoplasmacytic infiltrate, storiform fibrosis, and obliterative phlebitis, accompanied by increased IgG4-positive plasma cells and an elevated IgG4-positive/IgG-positive ratio [8,9]. However, the full triad may be incomplete in orbital specimens, and quantitative thresholds vary according to tissue type and diagnostic framework. Current criteria therefore emphasize integration of clinical and radiological findings, serum IgG4, histological morphology, immunostaining, and exclusion of alternative diagnoses [3,7-9].

In the present specimen, the dense plasmacytic infiltrate, numerous CD138-positive plasma cells, more than 20 IgG4-positive cells per high-power field, and low proliferative activity supported IgG4-related disease. Nevertheless, the absence of a reported IgG4/IgG ratio, serum IgG4 level, and explicit assessment of storiform fibrosis and obliterative phlebitis limits formal categorization. This limitation should be stated rather than overcome by assuming unavailable data. Moreover, IgG4-positive plasma cells can occur in other inflammatory conditions and in some lymphomas. The 2023 revised ophthalmic criteria particularly stress the need to exclude MALT lymphoma and other lymphoid malignancies [3].

The differential diagnosis of a superolateral orbital mass includes lymphoproliferative disorders, idiopathic orbital inflammation, lacrimal gland epithelial tumors, sarcoidosis, granulomatosis with polyangiitis, thyroid eye disease, infection, and metastatic disease. Lymphoma is especially important because it may coexist with or histologically resemble IgG4-ROD. A low Ki-67 index and the absence of a specific immunophenotypic pattern in the available panel favored a non-high-grade lymphoid process, but definitive exclusion of lymphoma may require assessment of light-chain restriction, clonality studies, and hematopathological review when morphology or clinical evolution remains suspicious [2,3,9].

Once the diagnosis is established, systemic evaluation is essential. In a 2025 nationwide multicenter study, extraorbital involvement was identified in more than half of adequately evaluated patients with definite IgG4-ROD, reinforcing the need to assess the pancreas, biliary tract, salivary glands, kidneys, lungs, lymph nodes, retroperitoneum, and large vessels according to the clinical context [4]. Serum IgG4 is useful but is neither perfectly sensitive nor specific; a normal value does not exclude tissue-proven disease [1,7,8].

Systemic glucocorticoids remain the usual first-line induction treatment for active symptomatic IgG4-ROD, particularly when vision, ocular motility, or other organs are threatened. The initial response is often rapid, but relapse during or after tapering is common [1,2,10,11]. Steroid-sparing immunomodulators may be considered in relapsing or steroid-dependent disease, although evidence for conventional agents is heterogeneous. B-cell depletion with rituximab has shown substantial activity in refractory, relapsing, or organ-threatening IgG4-RD and IgG4-ROD [1,10-12]. Surgery is primarily diagnostic, although selected patients may benefit from debulking; recent data suggest an association between debulking and remission, but surgery does not replace systemic assessment or medical treatment when active multisystem disease is present [4].

Long-term surveillance is required because clinical improvement does not eliminate the risk of relapse, fibrotic sequelae, optic neuropathy, or unrecognized systemic involvement. Follow-up should combine ophthalmic examination, assessment of visual acuity and ocular motility, serial imaging when indicated, and monitoring of systemic disease activity. In the next phase of management, we plan to complete the systemic work-up, initiate an appropriate treatment according to the findings, and ensure regular clinical and radiological follow-up.