Erythema nodosum (EN) is a common acute nodular septal panniculitis, characterized by the sudden onset of erythematous, firm, solid, deep nodules or plaques that are painful on palpation and mainly localized on extensor surfaces of the legs. These nodules are characterized by a typical histological appearance regardless of the etiology, marked by acute inflammation of the dermo-hypodermic junction and interlobular septa of the hypodermic fat, evolving without necrosis or sequelae.
Erythema nodosum is an acute, or recurrent hypersensitivity reaction to a variety of antigens with a clear female predominance that may be associated with several different stimuli or pathological conditions.
Erythema nodosum can occur due to a vast number of underlying causes including but not limited to idiopathic, infectious, and a variety of noninfectious causes as outlined below
Idiopathic: No obvious etiology have been found in about 30% to 50% of published cases
Non infectious causes
Inflammatory Bowel Disease
EN is the most common clinical form of the acute nodular hypodermis. It occurs more often in women between 25 and 40 years, but it can be observed at any age. Compared to men, women are affected three to six times more. It is rare without sex predominance in the pediatric population. Of worldwide ubiquitous distribution, there is, however, an ethnic and geographical difference in the incidences explained by the variation of triggering etiological factors. Familial cases have been reported and are usually caused by an infectious etiology.
EN is the result of a nonspecific cutaneous reaction to various antigens. The mechanism involved would be immunologically mediated. Numerous direct and indirect evidence supports the notion of type IV delayed hypersensitivity response to many antigens. It is postulated that the pathogenesis may be due to deposition of immune complex in the venules of subcutaneous fat, production of oxygen free radicals, TNF-alpha and granuloma formation. However, this hypothesis is not accepted by all authors.
Skin biopsy is not usually needed in the typical forms as a diagnosis can be reached from a detailed history and physical examination. Usual features suggestive EN include acute onset tender nodules on typical locations(most commonly on shins).
Skin biopsy is useless in typical forms. It is indicated in cases of unusual topography, the persistence of nodules several weeks, fistulization or atrophic scarring, and/or livedoid disposition of nodules. It highlights the involvement of interlobular septa by a lymphohistiocytic inflammatory infiltrate, sparing fat lobules and vessels. This aspect is invariable, whatever the etiology.
EN is characterized in a rather stereotyped way, whatever its cause, by the following evolutionary aspects:
EN never involves necrosis, ulceration, or scarring. It often evolves in several outbreaks, favored by orthostatism, and spreading out, at worst, over 4 to 8 weeks. The succession of outbreaks confers on the eruption a polymorphic appearance with knots of different ages, featuring the various shades of local biligenia.
The positive diagnosis of EN is primarily clinical. However, a thorough anamnesis (looking for tuberculous contagion, fever, bloody diarrhea, abdominal pain, respiratory problems, dysphagia, etc.) should be conducted as well as a complete clinical examination, always looking for associated signs.
In typical cases, a complementary investigation for positive diagnostic is not necessary. Nevertheless, it finds its place in the etiological diagnosis. Taking into account the above, the etiological assessment of an EN should include examinations according to the clinical orientation:
Extended rest is desirable and may require a work stoppage. Analgesics are prescribed on request. Venous compression reduces the pain felt in orthostatism. Steroidal anti-inflammatory drugs, colchicine (1 to 2 mg/day), may be prescribed until symptoms improve. Etiologic treatment is essential in some cases, and antibiotic therapy is needed in case of streptococcal infection or anti-tuberculosis treatment. In the case of Löfgren syndrome, pulmonary radiographic monitoring is recommended, because if mediastinal adenopathies disappear in a few months in most patients, sarcoidosis may persist in 10% of cases.
EN is a noisy but benign syndrome, with a spontaneously favorable course, which is related to an underlying condition that needs to be diagnosed by clinical examination and some complementary oriented tests. In addition to symptomatic treatment, that of the underlying condition may be necessary.