Psoriasiform dermatitis is a condition involving raised thin ridges on the skin lying beside long papillae, according to the National Center for Biotechnology Information. It causes itchiness and comprises a large group of related conditions.
Medical professionals can have a hard time diagnosing psoriasiform dermatitis even when using microscopes, reports the NCBI, as it is more a kind of pattern than one particular disease alone. As it can combine with other forms of dermatitis, the basic pattern may vary, and the patient's skin may also swell, as in spongiotic psoriasiform; show damage between various layers, as in psoriasiform lichenoid; or both, as seen in spongiotic psoriasiform lichenoid. If the pattern on the skin shows equal ridges and papillae, the dermatologist can diagnose the psoriasiform condition with more confidence. A doctor may use a blood test to look for the presence of white blood cells, often mixed with other cells, in order to confirm the patient's exact condition.
Part of the difficulty in diagnosis lies in the fact that many dermatologists only closely examine unusual psoriasis or areas of biopsied skin already treated, notes the NCBI. Consequently, they do not get to see what "normal" psoriasis looks like on the skin and before treatment. Because the patterns combine and even blood tests may look the same, a dermatologist may simply rely on looking at the skin to diagnose psoriasis rather than ordering a biopsy. Dermatologists have proposed different microscopic tests to increase the accuracy of diagnosis, as of 2015.