Barriers to an Accurate Diagnosis of Psoriasis

In this video, Abby Van Voorhees, MD, details the differential diagnoses of psoriasis, emphasizing "when in doubt, biopsy!" 

Dr Van Voorhees is professor and chair of dermatology at Eastern Virginia Medical School in Norfolk, VA. She is chair emeritus and a member of the National Psoriasis Foundation Medical Board.

Transcript
Dr Van Voorhees: Sometimes psoriasis is quite classic in its appearance. That's always nice when it's pretty clear that's what a patient has. Other times it can be much more nebulous, and the diseases that often trip us up.

Atopic dermatitis sometimes can look a whole lot like psoriasis. We tend to think of it for example, as involving the antecubital fossa, as opposed to the elbows like we see in psoriasis, but sometimes patients can have eczema that involves the elbows too. Especially for people who have very thin plaque, sometimes we can get confused between psoriasis and eczema. It's also sometimes a little harder in patients of color to make that distinction. That's definitely one that when I'm in that situation, sometimes I'll take a biopsy so then I know for sure which way I should be turning.

Seborrheic dermatitis is another place where people get confused, distinguishing between these two entities. In general, psoriasis tends to be a little more focal, so a little more isolated. You get a single spot. It can get thick and scaly, but then immediately adjacent normal skin is present. In contrast with seborrheic dermatitis, we see more classically that greasy scale that's more diffuse, not with such clear margins. Those two things can certainly overlap and be a little confusing. We especially see that confusion when we label this as sebopsoriasis, where we have some features of seborrhea and some features of psoriasis.

Mycosis fungoides is another one. While typically we see lesions of mycosis fungoides on the buttocks, it's not always the case. Again, sometimes that can be a little tricky to distinguish from psoriasis.

Lichen planus. You see that same scaling on Lichen planus. You don't see those polygonal papules, but sometimes when it's very extensive, I find that these two things can be a little confusing to distinguish. Happily, again, we can very much see the difference when we take a biopsy, so when in doubt, absolutely, that's a good rule of thumb.

PRP, or pityriasis rubra pilaris, can be a little tricky. The classic stigmata of PRP are those orange palms and soles, really thick hyperkeratosis in those areas. We see nail changes, and sometimes patients come in with nail changes, and it can be very difficult to say whether this is early PRP or psoriasis.

Actually, as we list them out, there are quite a few circumstances in which psoriasis can be challenging to distinguish from other inflammatory situations. Happily, most of the time that's not true. Happily, mostly we can see psoriasis and recognize it. I do believe that when there's any doubt, it's really important to take a biopsy because usually these different entities can be distinguished histologically. That allows for that clarity.