Primary Cutaneous CD4+ Small/Medium T-Cell Lymphoproliferative Disorder (PCSM-LPD): Dermoscopic Clues to Address Its Diagnosis and Their Interobserver Reliability

Background: Primary cutaneous CD4+ small/medium T-cell lymphoproliferative disorder (PCSM-LPD) is a rare lymphoid proliferation whose dermoscopic features are poorly defined, making diagnosis challenging. This study aims to identify the most common dermoscopic features of PCSM-LPD, assess their diagnostic accuracy, and evaluate interobserver reproducibility. Methods: We conducted a retrospective study in a referral clinic, including patients with histologically confirmed PCSM-LPD and a control group of various cutaneous lymphomas. Two experienced dermatologists independently reviewed dermoscopic images. Key dermoscopic features were identified and compared between the groups. Interoperator reproducibility was measured using Cohen’s Kappa. Diagnostic accuracy and agreement were the primary outcome measures. Results: We analysed 18 PCSM-LPD cases and 18 controls. Serpentine vessels were the most common feature in PCSM-LPD, with a sensitivity of 100% and specificity of 76.5%. Keratin plugs had a sensitivity of 88.9% and a specificity of 77.8%. A yellow-orange background was also significant, with 100% sensitivity and 77.8% specificity. Interoperator agreement showed low to moderate Kappa values, with better agreement for vessel presence and keratin plugs but lower for vessel type and distribution. Discussion: Serpentine vessels, keratin plugs, and yellow-orange background characteristics were found to be very sensitive and specific; however, their usability needs to be contextualised for diagnosing PCSM-LPD. Finally, despite high diagnostic accuracy, the interobserver agreement seems inconsistent, highlighting the need for standardised training. Further studies are necessary to validate these findings and improve diagnostic consistency in clinical practice.