Erythema nodosum

Erythema nodosum is a condition that causes painful, red bumps to appear on the skin, usually on the front of the legs. It affects the fat layer under the skin, which leads to inflammation and swelling. This condition is often a reaction to an infection, medication, or other health problems. The bumps can be tender and may feel warm to the touch. People with erythema nodosum might also experience fever, joint pain, and feeling generally unwell. It is not contagious and usually resolves on its own over several weeks. The main health impact is discomfort and sometimes difficulty walking due to the pain.

Erythema nodosum is an acute, inflammatory condition characterized by septal panniculitis without vasculitis, primarily affecting the subcutaneous fat. It is commonly triggered by a hypersensitivity reaction to various stimuli including infections (such as Streptococcus species, Mycobacterium tuberculosis), medications (e.g., sulfonamides, oral contraceptives), and systemic diseases like sarcoidosis or inflammatory bowel disease. Clinically, it presents as tender, erythematous nodules predominantly on the anterior shins. The pathophysiology involves immune complex deposition and subsequent inflammation of fat septa. It is significant as a marker of underlying systemic illness and can cause considerable pain and morbidity. Diagnosis is clinical but can be confirmed by skin biopsy showing characteristic histopathology. The condition is self-limited but may recur depending on the underlying cause.