Inflammatory dermatopathology is challenging to dermatopathologists as many diseases usually share one pattern. One should follow meticulously certain algorithms to limit the differential diagnosis to few diseases and also should pay attention to proper clinicopathological correlations to establish a definite diagnosis.

The psoriasiform pattern is one of those difficult patterns. I came across a nice article* which provides some clues to the diagnosis of this pattern and interestingly enough, I found myself adopting already most of these clues.

The first step in analyzing such pattern is to use the scanning magnification to assess whether it is a regular or irregular psoriasiform pattern, where regular hyperplasia usually points to psoriasis. At scanning magnification also we should assess the extent of the infiltrate: superficial only, or superficial and deep and its pattern: perivascular, lichenoid or nodular.

Another important point in evaluating this pattern is to decide whether this pattern is the sole pathology or is combined with other patterns (e.g. spongiotic or lichenoid), for each of them has a different cause.

Stratum corneum may provide clues also. Parakeratosis should be assessed if focal or confluent, if restricted to follicular ostia or not, if following specific patterns (e.g. checkerboard) and if it is associated with neutrophils or not. Fungal structures in the stratum corneum can be a simple and straightforward clue.

Careful examination of other layers of the epidermis (e.g. granular cell layer) and assessment of other findings (e.g. keratinocytes pallor or necrolysis) is also important.

Examining the dermal papillae for clues is also important (e.g. dilated tortous capillaries) and examination at higher magnification of the nature of the infiltrate and the predominant cell type also provides important clues. Finally, excluding epidermotropism and MF in any psoriasiform dermatitis is very important.

[b] [size=4]* Psoriasiform Dermatoses: Microscopic Approach[/size][/b]

[center]Rajalakshmi Tirumalae[/center]
[center]Indian Journal of Dermatology, 2013; 58(4): 290-293[/center]