Subcutaneous mycobacterial infection pathologically presented as erythema nodosum

Abstract

Erythema nodosum (EN) is an immunologic reaction to various stimuli, and characterized by inflammation of subcutaneous fat cells, resulting in tender red nodules and lumps. Mycobacterial infection is sometimes associated with its development. According to previous reports, the most common form of EN involves thickening of the superficial fascia of the cutaneous or subcutaneous fat layer. However, the two cases described here had a subcutaneous nodule in magnetic resonance images. Although in many cases, EN is idiopathic, treatment for a causative disease is needed when EN manifests in the presence of a specific disease. Therefore, if subcutaneous nodule or mass is diagnosed as EN histopathologically, underlying disease should be investigated to ensure appropriate treatment. Here, we report two cases of Mycobacterium tuberculosis or a nontuberculous Mycobacterial infection pathologically presented as EN and describe the MRI findings of subcutaneous Mycobacterial infection.