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Written by Azeen Sadeghian, MD, FAAD
Skin lymphoma refers to a broad group of lymphocyte neoplasms that exists in the skin. Any type of immune cell in the skin can become neoplastic, but the most common are T-cells. Cutaneous T-cell lymphoma (CTCL) is the most common form of skin lymphoma. It consists of various presenting signs and symptoms. The most common form of CTCL is mycosis fungoides. This category typically begins as patch-like plaques with fine scale and erythema. These are typically found in covered areas beneath clothing, such as torso and proximal extremities. It is often initially misdiagnosed as an eczema. Here are some clues that you should consider CTCL in your differential.
One of the classic presenting misdiagnoses of CTCL are the eczemas and its various forms--most commonly atopic dermatitis. The distribution of atopic dermatitis or other eczemas, including contact dermatitis, is unique and different from CTCL. For example, flexural regions such as antecubital or popliteal fossa are frequently involved in atopic dermatitis. Contact dermatitis tends to affect areas that are contacting the allergen or irritant. However, CTCL typically affects “double-covered” areas, meaning areas covered by clothing and underwear and are not exposed to the sun, such as the buttocks.
If the distribution does not align with the diagnosis you are considering, then consider whether CTCL should be in your differential.
Let’s say, for example, an older adult comes in to see you with a rash. Based on the history and exam, you're suspecting the diagnosis may be a form of eczema; however, their demographic does not match. They may have no preceding history of atopic dermatitis, eczema, or stigmata of any prior skin issues. In this situation, it’s prudent to consider CTCL, as many people with atopic dermatitis have stigmata of atopy in childhood. Patients with localized eczemas, such as contact or irritant dermatitis, tend to also fit into their own demographic of exposure, either occupational or environmental.
These patients should be monitored to ensure resolution and no recurrence, even after dry skin precautions and medical treatment.
Imagine you’ve done everything by the book but the rash keeps recurring. You’ve stopped oral drugs and personal care products that may be eliciting a skin reaction, you’ve initiated sensitive skin care precautions, the patient has used appropriate topical treatments, they are following your counseling, and yet the rash is still coming back. In this case, if CTCL fits in your differential, then you will need to consider a skin biopsy. It’s not uncommon for patients to need multiple biopsies over the course of years before a diagnosis can be established.
CTCL can be indolent and challenging to diagnose, particularly to the non-dermatologist. It’s important to note these three warning signs that should lead to its early suspicion.
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