Tehran University of Medical Sciences Case Reports in Clinical Practice 2538-2683 11 3 2026 09 28 139 142 Paniz Booshehri School of Medicine, Urmia University of Medical Sciences, Urmia, Iran. Anahita Majmaa Pediatric Critical Care Medicine Center, Children’s Medical Center and Hakim Children’s Hospital, Tehran University of Medical Sciences, Tehran, Iran. 2026 06 19 2026 08 18 Nicolau syndrome, also known as emboli cutis medicamentosa, is a rare but potentially severe complication of parenteral drug administration that may lead to acute pain, livedoid discoloration, and cutaneous or subcutaneous necrosis. We report the case of a 4-year-old boy who developed Nicolau syndrome shortly after intramuscular administration of benzathine penicillin for streptococcal pharyngitis. He presented with sudden severe pain, pallor, mottling, and livedoid changes involving the injected limb and adjacent regions. Prompt recognition and multidisciplinary conservative management, including anticoagulation, topical vasodilator therapy, corticosteroids, limb elevation, and intensive monitoring, were associated with progressive clinical improvement and preservation of limb function. This case highlights the importance of early diagnosis and timely supportive intervention in preventing severe ischemic complications of Nicolau syndrome. https://crcp.tums.ac.ir/index.php/crcp/article/view/1209 https://crcp.tums.ac.ir/index.php/crcp/article/download/1209/795