Rare Mimic of Conjunctivitis: Conjunctival Intraepithelial Sebaceous Carcinoma.

Sebaceous carcinoma, an uncommon malignant neoplasm, often arises de novo from periocular sebaceous glands. Commonly manifesting as diffuse eyelid thickening, sebaceous carcinoma can mimic other inflammatory processes such as persistent chalazion or blepharitis. Delayed diagnosis often complicates the disease course due to its indolent presentation. Described is a rare case of sebaceous carcinoma entirely confined to the conjunctival epithelium of the upper eyelid. An 80-year-old female presented for evaluation of bothersome "cysts" under her left upper lid as well as blurry vision in her left eye. The patient was repeatedly re-evaluated over the next few months and found to have Meibomian gland dysfunction of the upper and lower left eyelids as well as 3+ diffuse spongy papillary injection of the tarsal conjunctiva in the left upper lid, with large papillae and conjunctival thickening in the left inferior fornix. A conjunctival biopsy was eventually performed when appropriate management of presumed conjunctivitis failed to alleviate the patient's symptoms. Pathological examination of the left upper eyelid tarsal conjunctiva showed epithelium largely replaced by pagetoid spread of intraepithelial sebaceous carcinoma, with an underlying band-like lymphocytic infiltrate. The carcinoma was strongly adipophilin positive with variable EMA, PRAME, and Factor XIIIa positivity, confirming intraepithelial sebaceous carcinoma. The nuclei of the carcinoma had a smudged, salt-and-pepper appearance; however, CK20, INSM-1, and synaptophysin were negative, excluding Merkel cell carcinoma. A sebaceous carcinoma limited to conjunctival epithelium is rare. However, given its potential aggressive nature, it should be included in the differential diagnosis of "nonhealing conjunctivitis" or persistent unilateral irritation of the eyelid.