Objective: To compare expression of IHC Ki-67 in clinical variants of Psoriasis and Non- Psoriatic Psoriasiform Dermatoses (NPPD) and correlate immunohistochemical findings with clinical severity.

Methods: This prospective study was conducted over 18 months in the Department of Pathology at Muzaffarnagar Medical College, Uttar Pradesh. A total of 70 skin biopsy specimens with clinical diagnosis of Psoriasis (n=35) and Non- Psoriatic Psoriasiform Dermatoses (n=35) were included. Detailed clinical evaluation, histopathological examination and immunohistochemical staining for Ki-67 were performed. Statistical analysis was carried out using appropriate parametric and non-parametric tests and correlations with PASI score and Body surface area (BSA).

Results: The mean Ki-67 score was significantly higher in the Psoriasis group compared to the NPPD group (74 ± 5.0 vs 43 ± 7.0; p < 0.001). Classic histopathological features such as elongation of rete ridges, suprapapillary thinning, parakeratosis, diminished granular layer, vascular dilatation and Munro’s microabscesses were significantly more prominent in Psoriasis (p < 0.05). Ki-67 expression showed statistically significant correlation with PASI score and BSA involvement in Psoriasis. Strong correlations were observed between multiple histopathological parameters in Psoriasis, reflecting coordinated epidermal and dermal changes.

Conclusion: Ki-67 expression is significantly elevated in Psoriasis compared to NPPD, highlighting its diagnostic utility as an adjunct Immunohistochemical marker. However, its limited correlation with disease severity suggests that Ki-67 should be interpreted in conjunction with clinical and histopathological findings rather than as a standalone severity marker.

KEYWORDS: Psoriasis, Non-Psoriatic Psoriasiform Dermatoses, Ki-67, Immunohistochemistry, PASI, BSA.