Buerger stated that erythromelalgia is caused by a compensatory dilatation of superficial capillaries resulting from substantial luminal narrowing of larger arteries.¹ In a prospective single-center trial, Schwartz et al⁴ used noninvasive video microscopy to document qualitative morphologic characteristics of lower-extremity nutritional skin microcirculation in patients with atherosclerosis. Fourteen study participants with artherosclerosis and 11 age-matched control participants were assessed for capillary blood flow velocity, capillary diameter, and number of flow-active capillaries. The study participants were found to have a capillary blood flow velocity of 0.16 mm/s, capillary diameter of 10.5 µm, and 6.8 capillaries per field, whereas the control participants had a capillary blood flow velocity of 0.10 mm/s, capillary diameter of 8.7 µm, and 5.3 capillaries per field. These data support erythromelalgia as the clinical manifestation of a compensatory dilatation of superficial capillaries and of an increased number of flow-active capillaries. 

Placement of the healthy foot in the dependent position below heart level decreases capillary blood flow, and elevation produces no changes in flow.⁴ However, the same maneuver in patients with foot pain at rest and clinically significant atherosclerosis results in increased capillary blood flow with pedal dependency (ie, the patient is seated on an examination table with the foot in the down position) and decreased capillary blood flow on pedal elevation.⁴ The Buerger test should be used to evaluate patients suspected of having reduced circulation due to vascular obturation.¹ When administering this test, physicians should elevate the limb to be perpendicular to the horizontal plane, which would cause pallor in patients with clinically significant peripheral vascular disease.¹ On gradual lowering of the limb, the angle at which the color returns (ie, the angle of circulatory sufficiency) should be recorded.¹ In a variation of the Buerger test, the affected limb should be elevated to 60º from the horizontal plane for 2 minutes, and then the limb should be placed in the dependent position for another 2 minutes.⁵ Limb pallor during this test indicates peripheral artery disease, as does rubor in the dependent position. Although Buerger noted that the angle of the leg that results in pallor is a valuable adjunct in the recognition of the extent of circulatory disturbance and prognosis, no studies have been published, to the authors’ knowledge, that correlate specific angles to the degree of arterial occlusion. 

To better understand the diagnostic value of the Buerger test, Insall et al⁵ collected data among 55 patients (30 of whom had positive results using a variation of the Buerger test) with disabling claudication. The authors⁵ reported erythromelalgia in 43% of patients with a positive test result. Although 73% of patients who had a positive test result had palpable femoral pulses, popliteal and posterior tibial pulses were palpable in 7% of patients (no palpable dorsalis pedis pulses were detected). Arteriography demonstrated that 93% of arterial occlusions occurred below the inguinal ligament, and occlusions below the adductor hiatus were reported to be statistically significant among these patients (31% Buerger positive, 0% Buerger negative; P<.01).⁵ In a critical review of patients with suspected chronic ischemia of the lower extremities, McGee and Boyko³ reported a sensitivity of 100% and specificity of 54% of the Buerger test (positive likelihood ratio, 2.2; negative likelihood ratio, 0). 

The cumulative evidence from these studies suggests that the Buerger test may be highly sensitive for detecting arterial occlusions below the popliteal fossa but is not specific for arterial occlusion above the popliteal fossa. Although the specificity is low, the high sensitivity suggests that a positive Buerger test result indicates probable occlusive peripheral vascular disease. 

Physicians should consider using the Buerger test when peripheral vascular disease is suspected.^3,6 The finding of erythromelalgia remains distinct from erythema associated with skin and soft-tissue infections. When infection is present, tenderness, edema, and cutaneous warmth over the affected region will often be elicited, indicating necrosis or purulence complicating a gangrenous limb.⁷ Patients with skin and soft-tissue infections usually have a predisposing condition such as ulcers, wounds, cutaneous fissuring, or toe-web intertrigo, as well as a history of saphenous vein removal, radiation therapy, or venous stasis disease.⁷ Erythema due to infection will remain on elevation of the affected limb.⁷ The Buerger test emphasizes the continued importance of a meticulous bedside examination, which remains the touchstone of clinical medicine, even in an era of growing overreliance on expensive and often deleterious dye-based imaging studies.