What underlying condition is erythema nodosum commonly associated with?

Erythema nodosum is often associated with various underlying conditions, and one of the most significant associations is with tuberculosis. This condition is characterized by painful, red nodules that typically appear on the lower legs and is a form of panniculitis—an inflammation of the fat layer beneath the skin.

In cases of tuberculosis, particularly extrapulmonary forms or in the context of a hypersensitivity reaction to mycobacterial antigens, erythema nodosum can develop as a cutaneous manifestation of the underlying infection. The pathophysiology involves an immune response where the body reacts to the presence of the Mycobacterium tuberculosis organisms, leading to the characteristic skin lesions.

Diabetes mellitus, allergic rhinitis, and asthma are not typically associated with erythema nodosum. Diabetes can lead to a variety of skin conditions, but it is not specifically linked to the development of erythema nodosum. Allergic rhinitis and asthma are primarily respiratory conditions and do not have a direct connection to the inflammatory process that produces erythema nodosum. Thus, tuberculosis stands out as a notable underlying condition associated with this specific dermatological finding.