A Diagnostic Challenge: Severe Thrombocytopenia During Streptococcal Cellulitis Revealing Previously Unrecognized Immune Thrombocytopenia.

Severe thrombocytopenia is frequently encountered in patients with acute bacterial infections and is often attributed to infection-associated platelet consumption, potentially delaying recognition of alternative etiologies. We report the case of a 72-year-old man with chronic unexplained thrombocytopenia who presented with fever, generalized weakness, and progressive bilateral upper-extremity cellulitis, predominating in the left forearm where a chronic nonhealing fishhook injury had become secondarily infected, while the contralateral forearm demonstrated diffuse erythema, warmth, and swelling without an associated wound. Initial evaluation demonstrated leukocytosis, markedly elevated inflammatory markers, and profound thrombocytopenia with a platelet count of 12 ×103/µL. Imaging confirmed left forearm cellulitis without abscess formation or necrotizing soft tissue infection, and wound cultures grew Streptococcus pyogenes. The left forearm infection improved with targeted intravenous antimicrobial therapy, while the contralateral inflammatory changes gradually resolved; however, severe thrombocytopenia persisted despite multiple platelet transfusions. Further hematologic evaluation demonstrated a persistently elevated immature platelet fraction, giant platelets on peripheral smear, negative peripheral blood flow cytometry, and no laboratory evidence of thrombotic microangiopathy or disseminated intravascular coagulation, favoring peripheral immune-mediated platelet destruction over bone marrow failure or consumptive thrombocytopenia. High-dose corticosteroid therapy produced a rapid and sustained platelet recovery, confirming immune thrombocytopenia. This case highlights the importance of reconsidering the differential diagnosis when severe thrombocytopenia persists despite resolution of concurrent soft tissue infections. Failure to respond to platelet transfusions, together with evidence of preserved platelet production and corticosteroid responsiveness, should prompt early consideration of immune thrombocytopenia and facilitate timely initiation of appropriate immunosuppressive therapy while avoiding unnecessary diagnostic procedures and ineffective transfusion strategies.