Diagnostic yield of direct immunofluorescence testing in panniculitis: A retrospective cohort study of 87 specimens at a single institution

Summary: There is a dearth of evidence in the literature characterizing the utility of DIF for panniculitis. As such, this single-institution retrospective cohort study sought to evaluate the utility of DIF testing when clinical suspicion for panniculitis was present. A database of DIF specimens derived from patients seen at our institution (8/22/2017-11/30/2023) was filtered by clinical indication. All specimens containing any of the following terms within the clinical impression field were included: panniculitis, erythema nodosum, calciphylaxis, or lipodermatosclerosis. Retrospective chart review was conducted to determine the final diagnosis rendered after clinicopathologic correlation. Of 87 specimens obtained from 76 patients, DIF was negative or non-diagnostic in 86 (98.9%) and positive in one (1.1%). The singular positive DIF specimen revealed features suggestive of lupus erythematosus, and the patient from which this DIF was obtained was ultimately diagnosed with cutaneous polyarteritis nodosa (cPAN). Three specimens revealed a non-specific vascular pattern. Two of these were obtained from a single patient who had a final diagnosis of lupus panniculitis, while the third was obtained from a patient who was ultimately diagnosed with cPAN. Taken together, these findings suggest that DIF testing in the setting of clinically suspected panniculitis is low-yield diagnostically.