Acute-on-Chronic Limb Ischemia Mimicking Cellulitis: A Diagnostic Pitfall

Acute-on-chronic limb ischemia may present with clinical features that overlap with inflammatory conditions, potentially delaying recognition of arterial compromise. We report a case of an elderly woman with long-standing polycythemia treated with hydroxyurea who presented with progressive right foot pain, marked swelling, erythema, tenderness, and bluish discoloration of the hallux. She was discharged from the emergency department but returned the next night with worsening pain. Soft-tissue ultrasonography demonstrated diffuse subcutaneous edema without a localized collection, supporting an initial provisional diagnosis of cellulitis. Despite preserved motor function and sensation, progressive ischemic discoloration, prolonged capillary refill, and abnormal distal pulse findings prompted further vascular assessment. Computed tomography angiography (CTA) demonstrated a 6.2-cm right popliteal arterial thrombus with impaired distal perfusion. Her D-dimer was within the laboratory reference range at 0.40 µg/mL FEU, while the hematocrit was markedly elevated at 55.3%. Intravenous unfractionated heparin was initiated, resulting in improvement in pain and swelling and clinical stabilization, while definitive revascularization options were considered. The patient subsequently elected to pursue definitive treatment in her home country, precluding assessment of long-term limb-salvage outcomes. This case emphasizes the importance of careful and repeated vascular assessment in a painful, discolored limb, particularly before neuromotor deficits develop. Laboratory findings, including D-dimer, should be interpreted within their validated clinical context and should not supersede clinical evidence of impaired arterial perfusion.