Unilateral palpebral and bilateral orbital xanthogranuloma: An unusual presentation of adult-onset xanthogranuloma responding to tocilizumab.

Purpose: To report a rare presentation of adult-onset xanthogranuloma (AOX) with unilateral palpebral involvement and bilateral orbital disease, and to highlight the importance of systemic evaluation and the role of tocilizumab as an effective corticosteroid-sparing treatment. Observations: A 65-year-old woman presented with a two-year history of left-sided proptosis, periorbital swelling, and epiphora. Examination revealed a unilateral palpebral mass with bilateral orbital involvement, an atypical distribution for AOX. Imaging demonstrated bilateral extraocular muscle thickening and axial displacement of the left globe. Histopathology from an incisional biopsy showed xanthomatous histiocytes, Touton-type giant cells, and mature lymphocytes, consistent with xanthogranulomatous inflammation. Systemic evaluation revealed elevated serum IgG and pelvic lymphadenopathy. Due to disease progression and the need to minimize corticosteroid use, the patient was treated with tocilizumab, which led to clinical and radiological improvement. Surgical excision of the eyelid lesion was later performed for cosmetic reasons, with no evidence of recurrence to date. Follow-up PET-CT imaging, obtained three months after the final tocilizumab infusion, demonstrated complete resolution of prior orbital findings and no evidence of systemic involvement. Conclusion: This case illustrates a rare anatomical presentation of AOX with unilateral eyelid involvement and bilateral orbital extension. It underscores the importance of thorough systemic evaluation, long-term follow-up to monitor for progression to other AOXGD subtypes such as AAPOX, and the potential role of biologic agents like tocilizumab in achieving disease control while reducing corticosteroid exposure.