The value of using ultrasound to rule out deep vein thrombosis in cases of cellulitis

DOES WELLS SCORE WITH D-DIMER HELP DEFINE A LOW-RISK POPULATION?

The Wells clinical prediction rule is commonly used to assess the pretest probability of DVT in patients presenting with unilateral leg symptoms. The Wells score is often combined with D-dimer testing to help determine whether ultrasound is necessary. Studies of patients with suspected DVT have found that those considered low risk according to the Wells criteria had a 6.5% incidence of DVT.⁷ However, the predictive value is lower in the setting of presumed cellulitis. In a prospective cohort study of 200 patients with cellulitis, Maze et al.⁸ reported that use of the Wells score with D-dimer testing overestimated the DVT risk. D-dimer level was elevated for 74% of patients, and 20.5% were high-risk by Wells criteria. An algorithm determined that—among patients with a high-risk Wells score, a positive D-dimer result, or both—only 1 (0.5%) was diagnosed with ipsilateral DVT after ultrasound testing. Two patients were diagnosed with DVT in the contralateral leg. These results suggest that a strategy that incorporates the Wells score and D-dimer testing in the setting of acute cellulitis provides little value. The authors concluded that, in the absence of a known hypercoagulable state, ultrasound is not warranted. However, their study did not assess whether there are any specific hypercoagulable states for which further testing may be indicated.

WHEN MIGHT ULTRASOUND BE HELPFUL IN CELLULITIS?

Investigators have described possible DVT risk factors in patients with cellulitis, but definitive associations are lacking because of the insufficient number of patients studied.^8,9 The most consistently identified DVT risk factor is history of previous thromboembolism. In a retrospective analysis of patients with cellulitis, Afzal et al.⁶ found that, of the 66.8% who underwent ultrasound testing, 5.5% were identified as having concurrent DVT. The authors performed univariate analyses of 15 potential risk factors, including active malignancy, oral contraceptive pill use, recent hospitalization, and surgery. A higher incidence of DVT was found for patients with history of VTE (odds ratio [OR], 5.7; 95% confidence interval [CI], 2.3-13.7), calf swelling (OR, 4.5; 95% CI, 1.3-15.8), CVA (OR, 3.5; 95% CI, 1.2-10.1), or hypertension (OR, 3.5; 95% CI, 0.98-12.2). Given the wide confidence intervals, paucity of studies, and lack of definitive data in the setting of cellulitis, clinicians may want to consider the risk factors established in larger trials in other settings, including known immobility (OR, <2); thrombophilia, CHF, and CVA with hemiparesis (OR, 2-9); and trauma and recent surgery (OR, >10).¹⁰

WHAT YOU SHOULD DO INSTEAD

As the incidence of concurrent VTE in patients with cellulitis is low, the essential step is to make a clear diagnosis of cellulitis based on its established signs and symptoms. A 2-center trial of 145 patients found that cellulitis was diagnosed accurately by general medicine and emergency medicine physicians 72% of the time, with evaluation by dermatologists and infectious disease specialists used as the gold standard. Only 5% of the misdiagnosed patients were diagnosed with DVT; stasis dermatitis was the most common alternative diagnosis. Taking a thorough history may elicit risk factors consistent with cellulitis, such as a recent injury with a break in the skin. On examination, cellulitis should be suspected for patients with fever and localized pain, redness, swelling, and warmth—the cardinal signs of dolor, rubor, tumor, and calor. An injury or entry site and leukocytosis also support the diagnosis of cellulitis. Distinct margins of erythema on the skin are highly suspicious for erysipelas.¹¹ Other physical findings (eg, laceration, purulent drainage, lymphangitic spread, fluctuating mass) also are consistent with a diagnosis of cellulitis.

The patient’s history is also essential in determining whether any DVT risk factors are present. Past medical history of VTE or CVA, or recent history of surgery, immobility, or trauma, should alert the clinician to the possibility of DVT. Family history of VTE increases the likelihood of DVT. Acute shortness of breath or chest pain in the setting of concerning lower extremity findings for DVT should raise concern for DVT and concurrent PE.

If the classic features of cellulitis are present, empiric antibiotics should be initiated. Routine ultrasound testing for all patients with cellulitis is of low value. However, as the incidence of DVT in this population is not negligible, those with VTE risk factors should be targeted for testing. Studies in the setting of cellulitis provide little guidance regarding specific risk factors that can be used to determine who should undergo further testing. Given this limitation, we suggest that clinicians incorporate into their decision making the well-established VTE risk factors identified for large populations studied in other settings, such as the postoperative period. Specifically, clinicians should consider ultrasound testing for patients with cellulitis and prior history of VTE; immobility; thrombophilia, CHF, and CVA with hemiparesis; or trauma and recent surgery.^10-12 Ultrasound should also be considered for patients with cellulitis that does not improve and for patients whose localized symptoms worsen despite use of antibiotics.