Platelet-Rich Plasma Resultant Cutaneous Nodules on Scalp

A 36-year-old man developed asymptomatic subcutaneous nodules on his scalp after undergoing nine platelet-rich plasma (PRP) sessions for hair loss. The nodules appeared one year after the last PRP session and were diagnosed as PRP-induced benign non-Langerhans cell histiocytosis (non-LCH) of the skin. The nodules were characterized by CD68-positive histiocytes and were treated with topical clobetasol cream, but showed no change after three months. However, most lesions regressed spontaneously after six months. This case highlights a rare side effect of PRP therapy, suggesting that trauma and inflammation from frequent PRP injections may trigger histiocytic infiltration. Further studies are needed to understand PRP's effects at the tissue level.