We present a summary of a review of the subject from the people of Dermatology Therapy. It is very practical and concise.
EI presents clinically as recurrent crops of tender, violaceous nodules and plaques on the posterior lower legs. Lesions have also been reported on the feet, thighs, buttocks, and forearms. The nodules tend to evolve over several weeks, often developing focal ulceration and drainage. The areas heal with scarring and postinflammatory hyperpigmentation. The age of the patients in one review ranged from 13 to 66 years (mean 37 years). Although EI can occur in men, there is an overwhelming female predominance.
Histopathological examination most commonly shows diffuse septolobular panniculitis with primary neutrophilic vasculitis of nearby vessels. The classic vessel involved is a large muscular artery, but a systematic microscopic review of 101 biopsy specimens by Segura et al. showed the most common pattern to be vasculitis involving the small venules of the fat lobule (47% of cases).
There are varying degrees of acute and chronic inflammation, coagulative and caseation-like necrosis, and poorly developed granulomas. The simultaneous presence of both primary vasculitis and granulomas suggests a role for both type III and type IV hypersensitivities in the pathogenesis of EI.
EI was historically causally associated with tuberculosis because of frequent co-occurrence of the two diseases, although no mycobacterial organisms were ever identified onhistopathological examination. With the invention of the polymerase chain reaction technique in 1984, detection of minute quantities of antigen became possible. Beginning in the early 1990s with the development of specific primers able to distinguish Mycobacterium tuberculosis DNA from that of other species, there were several reports of detection of such material in lesions classified as EI or nodular vasculitis. However, EI has also been associated with both infectious nontuberculous and noninfectious disorders. Infectious nontuberculous cases have been associated with Nocardia, Pseudomonas, and Fusarium. There may also be an association with hepatitis B virus. Noninfectious associations may include previous episodes of superficial thrombophlebitis of the lower legs, hypothyroidism, chronic lymphocytic leukemia, rheumatoid arthritis, and Crohn’s disease. Finally, nodular vasculitis has been reported in association with treatment with propylthiouracil, with rapid resolution after the medication was discontinued.
As noted above, the vasculitic pathology of EI suggests a type III hypersensitivity reaction or immune complex-mediated vasculitis. Others have suggested that the reaction pattern more likely represents a type IV hypersensitivity reaction or a specific T lymphocyte-mediated response to an antigenic stimulus (mycobacterial or other). Indeed, patients with tuberculosis-associated EI can have an exaggerated response to intradermal purified protein derivative (PPD)-simulating cellulitis because of the extensive release of cytokines and chemokines by activated T lymphocytes.
Treatment of EI should target the underlying cause, if possible. All patients with suspected EI should receive an intradermal PPD application. Patients with positive tests should receive a full 9-month course of triple-agent antituberculous therapy under the care of an infectious disease specialist. Appropriate antimicrobial therapy should be provided for any other underlying infections, potentially associated systemic conditions should be treated, and any suspected medications should be discontinued if feasible.
Potassium iodide has also been reported as an effective treatment for EI. Further therapies are similar to the treatment of EN as described above: NSAIDs, rest, elevation, compression, and, possibly (in severe cases and once underlying infection has been ruled out) systemic corticosteroids may all be helpful. There are also isolated case reports of successful treatment of EI with mycophenolate mofetil and oral gold.