Erythema nodosum et multiforme

Erythema Nodosum et Multiforme refers to two distinct skin conditions that share some clinical features but have different causes, prognoses, and treatments. Erythema nodosum (EN) is characterized by tender, red nodules, primarily on the lower legs, while erythema multiforme (EM) presents with a rash that may look like targets (three concentric rings of color) on the skin, affecting both the limbs and the mucous membranes. Despite their differences, both conditions are considered reactive processes to various triggers, including infections, medications, and other underlying health issues.

Etiology

Erythema nodosum is often associated with infections such as streptococcal infections, tuberculosis, and fungal infections. It can also be a reaction to certain medications, including antibiotics and oral contraceptives, or related to systemic diseases like sarcoidosis, inflammatory bowel disease, and cancer.

Erythema multiforme, on the other hand, is commonly triggered by infections, notably herpes simplex virus (HSV) and mycoplasma pneumoniae. Drugs, such as sulfonamides, penicillins, and phenytoin, can also induce EM. Less frequently, it can be associated with systemic diseases or physical factors like radiation therapy.

Clinical Presentation

Erythema Nodosum: The hallmark of EN is the appearance of painful, red nodules, usually located on the anterior aspects of the lower legs. These nodules may also appear on the thighs and arms. Systemic symptoms such as fever, malaise, and arthralgias can accompany the skin manifestations.

Erythema Multiforme: EM is characterized by the sudden onset of symmetrical, red, target-like lesions on the skin. These lesions can be found anywhere on the body but are most common on the hands, feet, arms, legs, and face. In severe cases, EM can involve the mucous membranes, leading to conditions such as Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN), which are medical emergencies.

Diagnosis

Diagnosis of both conditions is primarily clinical, based on the characteristic appearance of the lesions. Biopsy may be performed to confirm the diagnosis and exclude other conditions. Additional tests, such as blood tests, throat cultures, and chest X-rays, may be conducted to identify underlying causes.

Treatment

Treatment of erythema nodosum focuses on addressing the underlying cause, if identified, and symptomatic relief. Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used to reduce pain and inflammation. Corticosteroids and potassium iodide are other treatment options.

For erythema multiforme, eliminating the triggering factor is crucial. Treatment may include antiviral drugs for HSV-associated EM, antibiotics for mycoplasma-induced cases, and discontinuation of causative medications. Supportive care and symptomatic treatment are important, especially in severe cases involving mucous membranes.

Prognosis

The prognosis for erythema nodosum is generally good, with most cases resolving without complication within six weeks. Chronic or recurrent cases may require further investigation for underlying conditions.

Erythema multiforme also tends to resolve spontaneously, but the prognosis can vary depending on the severity and the presence of mucosal involvement. Severe cases, such as SJS and TEN, require immediate medical attention due to the risk of significant morbidity and mortality.

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