PMLE/Actinic Prurigo

Polymorphous light eruption is a disease that is as easily made from the history as from the physical examination.  The salient history of the typical PMLE/AP patient is the onset of itching, burning and painful lesions that usually begin in the springtime, and often after a significant outdoor exposure.  The reason for this is complex, but I think of it as a true allergy to ultraviolet light.  There are good studies which show the lesions of PMLE (erythematous papules, patches and plaques on sun exposed skin) are very similar in their pathophysiology to Type IV cutaneous hypersensitivity (allergic contact dermatitis).  

In Native Americans (aka First Nations People if you are Canadian) this condition is usually referred to as Actinic Prurigo and is inherited in many tribes as an autosomal dominant condition with a very high penetrance.  It is more common in females.  In addition to the usual PMLE symptoms, they also have a cheilitis which mimics the vernal onset of the other symptoms.  The patient we saw in the pic was from the Pine Ridge Sioux Reservation, which is one of the more painful places in the US to live.  High degrees of alcoholism, child and spouse abuse, early pregnancy and illegal drug use makes the Pine Ridge Reservation a sad place, indeed. 

The history gives this away as PMLE, and there is no reasonable DDX other than solar urticaria, which has less of the vernal periodicity.  As a point of interest, we rarely see PMLE here in Florida because our chronic UV exposure hardens our skin to ultraviolet light and thus we don't get that exposure-loss of exposure-reexposure cycle that the northerners do.  

Many of you picked PMLE, and a couple picked Actinic Prurigo. Excellent work, everyone.