What IS that?

Those are key points to remember when dealing with rare skin conditions, according to Robert Auerbach, M.D., of New York, and Jeffrey Petersen, M.D., of St. Louis. They are two of the doctors who see the cases even other dermatologists have a hard time diagnosing.

They say a number of conditions are not easily recognized, often because they either resemble more common ailments or perhaps because they aren't technically dermatologic issues - but there are a number of ways dermatologists can approach these rare, and sometimes fatal, conditions.

Bullous bafflers

Bullous eruptions are one category of dermatologic conditions that contains both common and less serious varieties, as well as some serious and very rare presentations.

Dr. Auerbach warns, "It's true that if you look at a thousand cases of blistering eruptions you're going to have everything from shingles to herpes simplex to poison ivy, which are of limited significance, but you have to make sure that what the patient has is not something else.

"Most dermatologists can differentiate between those and a significant bullous disease, but many nondermatologists can miss them. If doctors don't know what they are looking at, they really have no choice but to refer it."

According to Dr. Auerbach, those referrals should be made quickly, because for some bullous conditions, time is of the essence.

Toxic epidermal necrolysis

"Toxic epidermal necrolysis (TEN) has a 30 percent mortality rate - more, if the patients are very young or very old or sick - so any appearance of blisters demands a prompt diagnosis.

"Luckily, we have a treatment today, but it only works early in the game, before sepsis and multi-organ failure set in - and that can occur rapidly."

Although currently rare, TEN is expected to become more common Dr. Auerbach says.

"One of the AIDS drugs has an extremely high incidence. Sulfa drugs also have a high incidence and they are being used more often because of methicillin-resistant Staphylococcus aureus (MSRA)."

Cicatricial pemphigoid

Cicatricial pemphigoid occurs rarely, but constitutes a serious health threat.

It can scar the esophagus so the patient can't eat, or even swallow his or her own saliva. It can also scar the conjunctiva and cause blindness. Steroids may have a limited effect, and immunosuppressants may work, but potentially with serious side effects. Dr. Auerbach says doctors are starting to use biologics, but with trepidation.

"The problem is, the reports are anecdotal," he says.

Merkle cell tumors

Merkle cell tumors also require expeditious diagnosis.

"It's a terrible tumor which can move rapidly, is not easily recognized, and can kill," he says.

The tumor appears as a red bump that looks like an old cyst that is inflamed, and can be overlooked until too late. The Merkle cell tumor is diagnosed through biopsy and treated with surgery if found early enough.