Cutaneous lupus erythematosus simulating squamous neoplasia: the clinicopathologic conundrum and histopathologic pitfalls.

Background The clinical distribution and character of cutaneous lupus erythematosus lesions can simulate squamous neoplasms, leading physicians to submit a shave biopsy specimen with a differential diagnosis of squamous neoplasm. Objective Our aim was to describe histologic features of interface dermatitis that cause difficulty in distinguishing between cutaneous lupus erythematosus and squamous neoplasia in shave biopsy specimens and to identify distinguishing criteria. Methods Twenty-six biopsy specimens from 10 patients initially diagnosed with squamous neoplasia that ultimately proved to be cutaneous lupus erythematosus were identified. Comparisons were made of these to 38 control biopsies of chronic cutaneous lupus erythematosus and 34 control biopsies of keratoses/carcinomas without lupus. All biopsies were scored (0 or 1: absent or present) with respect to 11 histologic criteria. Results The criteria of perifollicular inflammation, follicular plugging, vacuolar interface change, compact orthokeratosis, and acrosyringeal inflammation were significantly more common in the lupus cases than in the keratoses/carcinomas controls. The mean lupus case score was 6.88, lupus control score 6.55, and keratoses/carcinomas control score 5.08. Limitations A limited number of patients were studied. Microscopic observations and assumptions with inherent subjectivity were used in establishing the histologic scores. Conclusion Use of the criteria presented, although not absolute, should alert one to the possibility of lupus in an atypical squamous proliferation, especially in suspected squamous neoplasms that worsen or recur after therapy.