Histopathology of ethnic skin, other conditions

Chicago - Although there are not many histologic differences in black and white skin, those that do exist are associated with different presentations and consequences in certain ethnic populations.

That was part of Jacqueline M. Junkins-Hopkins M.D.'s message at the American Academy of Dermatology's Academy '05, here. She is assistant professor of dermatology, University of Pennsylvania.

"One of the main differences is in the color of ethnic skin, which is not due to the number of melanocytes, but instead, the type of melanosomes, and how they aggregate in the skin, and the amount of melanin transferred to the keratinocytes."

According to Dr. Hopkins, dermatologists need to understand that certain conditions result in more prominent dyschromia in patients with darker skin. This is especially apparent in conditions that destroy the basal layer of skin.

Such conditions that may result in accentuated post-inflammatory pigment in ethnic patients include lichen planus and lupus erythematosus.

Hair follicles in some patients with ethnic skin contain more melanin, thus acne-associated inflammation of the follicle may lead to incontinence of pigment into the deeper dermis, and more prominent and persistent post-inflammatory pigment.

Pitfalls of diagnosing

Dr. Hopkins says some common dermatoses that occur in ethnic skin can present special difficulties in diagnosis.

She says two skin malignancies seen in patients with skin of color that may be difficult to diagnose histologically are mycosis fungoides and acral lentiginous melanoma.

Mycosis fungoides (MF) is a cutaneous T-cell lymphoma (CTCL), which often presents as a hypopigmented variant in patients with ethnic skin.

Dr. Hopkins says this variant of CTCL tends to occur in Hispanics and blacks.

It presents as faint, ill-defined, hypopigmented patches that typically occur on the extremities, the buttocks and trunk," she tells Dermatology Times. "It may present at a young age, in teenagers and young adults, but may not immediately be diagnosed in this age group. Patients can present for years without a definitive diagnosis, due to clinical overlap of hypopigmented MF with pityriasis alba."

In contrast to other types of non-melanoma skin cancers, which are sun-induced, this condition is actually UV responsive.

Dr. Hopkins says the diagnosis can be difficult.

Patients can have multiple persistent hypopigmented patches, especially on double-covered areas such as the buttocks and trunk, which respond to steroids, but recur at the same spot," she says. "The biopsy may be equivocal in early disease. If the doctor thinks, clinically, the patient has MF, options are available to help make the diagnosis.

"A sample can be sent for polymerase chain analysis of the T-cell receptor gene to look for a monoclonal gene rearrangement."

Assessment for an abnormal immunophenotype by immunohistochemical staining can also be done. Most patients with MF have a CD4 or a T-helper phenotype of their lymphocytes, but some patients with the hypopigmented variant, in contrast, have a CD8 phenotype.

"That's something to keep in mind when assessing the immunophenotype; thus, if the helper:suppressor ratio is not elevated - it might be due to the CD8 phenotype, in contrast to a reactive T-cell profile.

"Because dermatopathologists are more attuned to some of the subtleties of the diagnosis, one should ensure that biopsies taken to diagnose early MF should be assessed by someone trained in this specialty."

Vitiligo overlap

The condition can also overlap with vitiligo, and Dr. Hopkins says that's another condition that can present difficulties in diagnosis.

Early vitiligo can have an inflammatory reaction and can look like inflammatory dermatoses under the microscope, Dr. Hopkins says, even if clinically it doesn't look inflamed. That may make it hard to differentiate from other types of post-inflammatory pigmentation."