Melanin & More
Dr. Okoye
Because skin diseases are so often diagnosed when erythema appears, darker skin can make identifying a problem more difficult, said Dr. Okoye.
“Melanin can mask erythema, it can mask redness, and we’re taught to look for redness when we’re trying to diagnose skin conditions,” she said. “And so if [the patient’s] melanin is masking that, it can lead to delays to diagnosis.” In people with darker skin, erythema could be red or purple, but it could also be dark brown, or bluish-black, she said.
She discussed a patient of color with psoriasis, who, like many other patients, had some erythema but the redness was not the most prominent feature, “so really we’re relying on some of the other patterns that we see in skin disease” for diagnosis. These include the location of plaques and whether there is scaling, she said.
Dr. Okoye said clinicians should be comfortable ordering a biopsy when they are unsure what they are seeing on their physical exams. Since coming to Howard University, she said, “I have biopsied more psoriasis that I had in my career up until that point because I’d been fooled so many times.”
She discussed a patient with psoriasis on her scalp who had been diagnosed with seborrheic dermatitis for many years, with the only give-away being the pits in her nails. In these kinds of cases, with psoriasis involving the scalp in patients of African descent and with curly hair, she prescribes biologics very early on because the challenge of maintaining this hair type with psoriasis leads to quality-of-life struggles.
In a patient she discussed involving juvenile dermatomyositis, which typically involves a purplish heliotrope rash as a telltale sign, there was “no purple to be found.” Instead, there was only subtle hyperpigmentation and hypopigmentation.
“When you compare this to what we’re taught to look for in the heliotriope rash, it can be easy to miss—and indeed this was missed for a long time,” said Dr. Okoye.
A “trick” she uses to more easily identify erythema in people with darker skin is to examine them with a blue background—with a blue sheet of paper or blue fabric—which “usually makes the redness stand out a little bit more.” She also said that photos taken with a phone can sometimes allow a clinician to see redness even better than they can see with their own eyes.
She also said that, due to a crosstalk between melanocytes and fibroblasts, hypopigmentation or depigmentation can be a sign of fibrosis or scarring.1
“I think I see this the most, in the salt-and-pepper pigmentation of scleroderma, where the areas of fibrosis can lose pigment altogether,” she said.
Pigmentation can also be used to track someone’s response to therapy, she said.
Focus on Scleroderma
Dr. Hummers
Dr. Hummers said that many diseases can look a lot like scleroderma at first blush, forcing clinicians to be alert to telling distinctions.2
“Most of these diagnoses are clinically distinguishable without biopsy if you just think about some of these things,” she said.
She showed a photo of a hand that had some skin tightness and some pigmentary changes. “If you just looked at that hand, we would often say, ‘Well, that looks like systemic sclerosis,’” she said. “But that person has scleromyxedema.”
This disease, she said, is the “most scleroderma-like” of the mimics, with a distribution that is very similar but with the exceptions that it involves prominent skin changes around the ear, almost always with papules, and it does not spare the back, while scleroderma does. The skin quality resembles scleroderma as well, but with a “papular quality” and with the papules sometimes coalescing, leaving the skin just feeling thick, she said.
According to Dr. Hummers, a biopsy may help, but if one is ordered, a mucin stain should be specifically requested.
Diffuse scleroderma involves nearly the whole body, but it spares the mid-back, almost always spreads in a distal to proximal direction and always involves the fingers. The skin quality is thick and waxy and difficult to pinch, she said.
She emphasized the importance of including RNA polymerase III in labs becauseit’s linked to the risk of progression, the risk of a renal crisis and the presence of cancer.
“If you’re not routinely checking this, please check this antibody; it’s so important,” she said.
With limited scleroderma, patients often have Raynaud’s syndrome for years before other symptoms or recognition of disease, and skin thickening is usually limited to the fingers. These patients do not need treatment directed at the skin.
“We really need to avoid immunosuppression in most of these patients,” Dr. Hummers said.
Scleredema almost always starts at the back of the neck, on the upper back and around the shoulders, possibly progressing to the chest, back and upper arms. It feels what Dr. Hummers called “doughy” when you pinch it.
“It’s clear thick, but it feels doughier than scleroderma does,” she said. It most often occurs in the setting of poorly controlled Type 2 diabetes.
Eosinophilic fasciitis has a distribution in the extremities and the trunk but usually spares the hands and feet. Its skin quality is “woody” and deep, Dr. Hummers said.
“You should be able to pinch the skin but it feels thick under, so you can almost push the skin over this thickened fascia,” she said.
Peripheral eosinophilia can be found sometimes, but she cautioned this will disappear even with a bit of steroid treatment, so its absence doesn’t rule out eosinophilic fasciitis.
“If you see somebody who you know has morphea, you should really also kind of feel for eosinophilic fasciitis changes,” she said, because this may trigger treatment with corticosteroids. She also said there have been many reports of eosinophilic fasciitis after the use of checkpoint inhibitors.
Thomas R. Collins is a freelance medical writer based in Florida.
References
- Shen Z, Shao J, Sun J, Xu J. Exosomes released by melanocytes modulate fibroblasts to promote keloid formation: A pilot study. J Zhejiang Univ Sci B. 2022 Aug 15;23(8):699–704.
- Morgan N, Hummers LK. Scleroderma mimickers. Curr Treatm Op Rheumatol. 2016 Mar; 2(1): 69–84.
