# Conjunctival Intraepithelial Neoplasia With IgG and Complement Deposition: Spurious Association or Biologically Explainable?

## TL;DR

A case of conjunctival intraepithelial neoplasia showed unexpected immune deposits, raising questions about false positives in autoimmune disease testing.

## Contribution

Reports a rare case of CIN with IgG and C3 deposition, highlighting potential false positives in DIF testing.

## Key findings

- A CIN case showed IgG and C3 deposition in the basement membrane zone via DIF.
- The patient had no signs of autoimmune blistering disease.
- False-positive DIF results may occur in conjunctival neoplasia.

## Abstract

Conjunctival intraepithelial squamous neoplasia (CIN) is a premalignant ocular surface lesion typically diagnosed by clinical features and confirmed with routine histopathologic examination, rather than immunofluorescence studies. Direct immunofluorescence (DIF) of conjunctival tissue is most commonly used to support the diagnosis of autoimmune blistering diseases, particularly mucous membrane pemphigoid, by identifying immunoreactant deposition along the basement membrane zone (BMZ). However, such findings are not expected in CIN and may complicate interpretation.

We report a case of CIN with unexpected positive DIF findings of IgG and C3 in the BMZ. A 63-year-old man with a clinically apparent conjunctival lesion underwent biopsy, which confirmed CIN on routine histopathology. A portion of the specimen was inadvertently submitted for DIF, revealing linear deposition of IgG and C3 along the conjunctival BMZ. The patient had no clinical history or examination findings suggestive of mucous membrane pemphigoid, other autoimmune blistering disease, or systemic inflammatory disorder that could account for these immunoreactant deposits. This association suggests nonspecific deposition of immunoglobulins and complement in the setting of conjunctival neoplasia, a phenomenon rarely reported in the literature. This case highlights the potential for false-positive DIF results in conjunctival lesions and emphasizes the importance of submitting a concomitant biopsy for routine light microscopy when ordering DIF in patients with suspected mucous membrane pemphigoid to ensure accurate diagnosis.