Erythema induratum

Erythema induratum is a skin condition characterized by the presence of nodular eruptions, primarily on the posterior aspect of the lower legs. It is considered a form of vasculitis and is closely associated with tuberculosis (TB). The condition is more commonly observed in women and often correlates with periods of cold weather. Erythema induratum is also referred to as Erythema induratum of Bazin, named after the French dermatologist Pierre-Antoine-Ernest Bazin who first described the condition in the mid-19th century.

Etiology

Erythema induratum is believed to be a hypersensitivity reaction to Mycobacterium tuberculosis or its antigens. However, not all cases are linked to tuberculosis, and the condition can also be idiopathic or associated with other bacterial infections. The pathogenesis involves a delayed hypersensitivity reaction leading to vasculitis and subsequent nodular lesions.

Clinical Presentation

Patients with erythema induratum typically present with tender, red to violaceous nodules on the calves. These nodules may ulcerate, leading to painful ulcers that heal slowly, often leaving atrophic scars. The condition is chronic and relapsing, with episodes more frequently occurring in colder months.

Diagnosis

The diagnosis of erythema induratum is primarily clinical, supported by histopathological findings. A biopsy of the lesion typically shows lobular panniculitis with vasculitis. Special stains for Mycobacterium tuberculosis, such as Ziehl-Neelsen stain, may be used to identify mycobacterial DNA in tissue samples. Additional tests, including tuberculin skin test (Mantoux test) and interferon-gamma release assays (IGRAs), can help establish a link to tuberculosis.

Treatment

The management of erythema induratum involves addressing the underlying tuberculosis infection, if present, with appropriate antituberculous therapy. Non-tuberculous cases may be treated with a combination of anti-inflammatory agents, such as nonsteroidal anti-inflammatory drugs (NSAIDs), and immunosuppressive medications like corticosteroids. Supportive measures, including compression stockings and avoidance of cold exposure, are also recommended.

Prognosis

With appropriate treatment, the prognosis for erythema induratum is generally good. Lesions typically resolve over weeks to months, although relapses are common. Long-term follow-up is necessary to monitor for recurrence and manage any underlying conditions.

Epidemiology

Erythema induratum is rare, with a higher prevalence in countries with endemic tuberculosis. It predominantly affects middle-aged women, although cases have been reported in all age groups and genders.