Solitary erythematous round nodule with a hemorrhagic crust on the posterior shoulder.

Primary cutaneous CD4+ small/medium-sized pleomorphic T-cell lymphoproliferative disorder (PCMS-TCL) is a rare skin condition. We present a 67-year-old patient with a growing lesion on the shoulder that was diagnosed as PCMS-TCL. The patient was otherwise healthy without systemic involvement. The lesion was surgically excised, and no recurrence occurred. PCMS-TCL has an excellent prognosis, unlike other cutaneous lymphomas. This case highlights the importance of crafting a comprehensive differential diagnosis that incorporates any possibilities of rare disorders like PCMS-TCL to avoid unnecessary treatment.