Diagnostic Ambiguity of Distal DVT (dDVT) Misdiagnosed as Nonpurulent Lower Extremity Cellulitis (NLEC): A Case Study

Suwanee, GA

Introduction

Given the lack of a definitive diagnostic test for cellulitis, about 39% of cases are misdiagnosed. The repercussions of misdiagnosing nonpurulent lower extremity cellulitis (NLEC) for deep vein thrombosis (DVT) can be grave, considering the potential risk of pulmonary embolism (PE). While distal DVT (dDVT) is associated with <5% of PE formation, about 25% of untreated dDVT can ascend to the proximal leg veins; whereas 50% of proximal DVTs (pDVT) progress to PE development within a 3-month timeframe.

Case Report

A 50-year-old female presents to her PCP with a right medial ankle rash for 2 days. She denies inciting events, fever, chest pain, dyspnea, weeping lesions, or swelling. Past medical history includes obesity and controlled diabetes mellitus. Vitals are normal. Examination reveals a 10 x 6 cm blanchable, erythematous rash of the right distal medial lower leg. It is warm and tender to touch, without obvious edema. She demonstrates full ankle ROM. Homans sign is negative. Oral cephalexin, warm compresses, and good glycemic control are advised for suspected NLEC. After 24-hours she endorses no symptomatic improvement, therefore doxycycline is added for MRSA coverage. After another 24-hours of persisting symptoms, she presents to the ED where a right lower extremity venous duplex reveals a posterior tibial vein thrombosis. Antibiotics are discontinued and a vascular specialist manages her conservatively with subcutaneous enoxaparin until uncomplicated resolution of symptoms.

Discussion/Conclusion

DVT and NLEC share several overlapping symptoms including erythema, swelling, warmth, and pain. However, the incidence of NLEC is twice as common as DVT, with dDVT and pDVT accounting for 20% and 80% of DVT cases, respectively. While Homans sign is easily performed during examination, it is positive in only 33% of patients with DVT and falsely positive in 21% without DVT. Conducting an age-adjusted D-dimer assay is reasonable for a patient with a low pretest probability for DVT, but it is not reliable in distinguishing between cellulitis and DVT since infectious processes can also cause elevated D-dimer levels. Compression ultrasonography (CUS) is beneficial in evaluating for DVT, but challenges lie in the examination of distal veins, which have poor sensitivity (43% to 56.8%) yet high specificity (95% to 97.8%). Duplex US (DUS), conversely, has a 71.2% sensitivity and 94.0% specificity for dDVT. Although DUS is fast and noninvasive, it must be performed by skilled technicians as examination of distal veins via US might pose greater technical difficulty yielding lower positive rates, with up to 50% false negatives.

Ultimately, although US may be helpful in distinguishing dDVT from NLEC, the Infectious Disease Society of America (IDSA) practice guidelines currently do not recommend imaging suspected areas of infection unless the patient has afebrile neutropenia, but rather recommend empiric antibiotic treatment for suspected NLEC. Following initiation of antibiotics, resolution of symptoms should be seen within 24-48 hours, thus failure of symptom resolution should warrant additional workup to rule out NLEC mimics, such as DVT.