Objectives: To identify the clinical and histological features of MF that can assist in distinguishing MF from MF-mimicking cases. Although mycosis fungoides (MF) is the most common subtype of cutaneous T-cell lymphoma, clinicopathological correlations are required to establish an accurate diagnosis, which are currently lacking. Methods: This retrospective observational study evaluated the clinical presentations, characteristics, and histological features of 56 patients with suspected MF who presented to our clinic between January 2018 and August 2022. Immunohistochemistry was performed, and the loss of CD5 and CD7 T-cells and T-cell receptor rearrangement was evaluated. Results: Overall, 34 patients were diagnosed with MF, whereas 22 were not. Clinical erythroderma, poikiloderma, and nodular presentations were more commonly associated with a histological diagnosis of MF than macular presentations. Erythema and pruritus were significantly more common in MF cases than in MF-mimicking cases (p<0.05). Epidermotropism and parakeratosis were the key histological features for diagnosing MF. Additionally, Pautrier’s microabscesses correlated with the clinical presentation of plaques in MF. Loss of CD7 expression on the T-cell surface was observed even in early-stage MF cases. Conclusion: Our proposed diagnostic features are statistically valid and, along with those previously reported, can aid in identifying and distinguishing MF cases from MF-mimicking cases.

Piebaldism is a rare genetic disorder caused by KIT mutations and clinically characterized by fixed depigmented patches throughout the body. Herein, a case of piebaldism in which the depigmented patches regressed as the patient grew older, along with the development of multiple café-au-lait macules, is described. The likely pathogenic, heterozygous KIT c.1991-2A>G variant was detected as the potential cause of this unusual piebaldism phenotype. This case provides new knowledge on genotype-phenotype correlation of KIT mutations for piebaldism etiology and presentation.

Psoriasis and rheumatoid arthritis (RA) are common chronic diseases with distinctive histological and molecular features. However, there are similarities in their immunological pathogenesis, leading to the use of some similar systemic biological treatment. In 5% of patients using biological therapy such as the anti-tumor necrosis factor alpha (anti-TNF-α), a paradoxical reaction (i.e., the exacerbation or development of one disease while treating the other) may develop. We report a case of a 27-year-old female diagnosed with seropositive RA who developed paradoxical psoriasis (PP) after the use of Adalimumab, an anti-TNF-α, and paradoxical eczema due to the use of Ixekizumab, an anti-interleukin-17A, for the treatment of PP. This case demonstrates the occurrence of two different types of paradoxical skin reactions in a single patient. This case also highlights the importance of the selection and cessation of biological treatment in similar cases, as well as the factors that might predict the development of paradoxical reactions to promote the safe usage of biological therapy.