EXPERT ANALYSIS AT THE SUMMER MEETING OF THE AMERICAN ACADEMY OF DERMATOLOGY

NEW YORK – Both dermatologists and pathologists can make the mistake of diagnosing a long list of pseudolymphomas as lymphomas, according to Dr. Antonio Subtil, who is an associate professor of dermatology and pathology at Yale University School of Medicine, New Haven, Connecticut.

The diagnosis is not trustworthy without agreement by a team of experts, he said. Most dermatologists do not have sufficient expertise in histopathology to interpret equivocal findings. Pathologists do not typically grasp subtleties in dermatologic presentations that may also be critical to reach an accurate diagnosis regardless of histopathology.

Mycosis fungoides (MF) represents almost 60% of cutaneous T-cell lymphomas (CTCL), but only a proportion of patients with MF have a classic presentation and the extensive array of other T-cell and B-cell lesions constitute a heterogeneous profile of lesions, according to Dr. Subtil, who spoke on skin lymphoma knowledge gaps at the summer meeting of the American Academy of Dermatology (AAD). The biases of the dermatologist and the pathologist in isolation can lead to misdiagnosis, which is the reason to insist on a clear correlation between pathologic and clinical findings.

Speaking as a dermatologist, Dr. Subtil cautioned that pathologists “do not understand our terminology” and are not facile in differentiating clinical descriptions of cutaneous lesions. Speaking as a pathologist, Dr. Subtil cautioned that “I cannot trust a pathological report by itself” without understanding the clinical context.

As an example, he recounted a case of an ulcerated nodule that proved to have a lymphoid infiltrate on biopsy. When cells in the infiltrate were found to be CD30+, the likely diagnosis appeared to be an anaplastic large cell lymphoma. Only further testing revealed molluscum contagiosum, which can have a similar appearance and also feature CD30+ cells. A course of unnecessary chemotherapy was narrowly averted.

A small sample of the pseudolymphomas that can fool the clinician include lymphomatoid drug eruption, cutaneous leishmaniasis, lymphomatoid lichenoid keratosis, and reactive lymphoid hyperplasia at the site of vaccination, according to Dr. Subtil. He outlined a series of challenges that should be recognized before settling on a diagnosis.

One of the most important of these challenges is the limited specificity and sensitivity of any clinical characteristic or diagnostic study in isolation, according to Dr. Subtil. Even tissue studies with polymerase chain reaction (PCR) are associated with false positive and false negative results and, like everything else, must be evaluated in the context of the pathological and clinical findings.

Another challenge to a definitive diagnosis is the overuse of the term “atypical” by both dermatologists and pathologists. Dr. Subtil called the propensity to use this label the “atypical syndrome” and cautioned that it may sometimes be an obstacle for seeking a more definitive description of the underlying pathology. Using a team approach, which Dr. Subtil suggested might also include a hematologist and an oncologist, to reach consensus about the diagnosis substantially reduces the risk of a misdiagnosis.

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