CASE REPORT

An African American man in his 70s presented with more than a 20-year history of firm nodules on the left calf. In addition, he reported a 6-month history of new-onset tender nodules on the posterior lower extremities and thighs. He denied systemic symptoms such as fevers, chills, or pulmonary or gastrointestinal symptoms. His past medical history was significant for Hepatitis C, treated breast cancer, and an untreated positive purified protein derivative test for tuberculosis. On physical examination, multiple deep subcutaneous nodules were scattered on the bilateral lower extremities. There was a hyperpigmented patch overlying a crop of nodules on the left calf (Figure 1). An interferon gamma release assay was positive, and chest x-ray was normal, consistent with latent tuberculosis. A punch biopsy of a nodule on the left hip was performed, which revealed a diffuse septolobular panniculitis (Figure 2 and Figure 3). The infiltrate consisted of lymphocytes, macrophages, and poorly formed granulomas. Septal fibrosis was seen. In addition, there was vasculitis involving the small venules. Given the clinical and histopathologic findings, he was diagnosed with erythema induratum. He was initiated on a 9-month course of isoniazid and had resolution of the lower extremity nodules after 5 months of treatment.

FIGURE 1. Hyperpigmented patch on the left calf overlying a group of subcutaneous nodules.

FIGURE 2. Deep-seated subcutaneous tender nodule on the left hip.

FIGURE 3. Hematoxylin and Eosin stain, original magnification of 100. Microscopic examination revealed a diffuse, septolobular panniculitis. The infiltrate was lymphocytic with poorly formed granulomas.

DISCUSSION

Erythema induratum is synonymous with nodular vasculitis. When of tuberculous etiology, it has been called Bazin's disease or erythema induratum of Bazin; in nontuberculous cases, it is referred to as erythema induratum of Whitfield (Whitfield, 1901). The disease was first described by Bazin in 1861 as subcutaneous, indurated, erythematous nodules on the posterior lower legs of women (Bazin, 1861).

Epidemiologically, erythema induratum is an extremely rare diagnosis. The disease has a female predominance of up to 90% (Bolognia, Jorizzo, & Schaffer, 2012). There is no racial predilection. Affected patients are usually middle aged with a mean in the fourth decade of life, although the range is wide, and pediatric cases have been reported. Erythema induratum of Bazin is more common in populations where tuberculosis is endemic (Bolognia et al., 2012).

The lesions are usually painful but may be tender only on palpation or may be asymptomatic. Although they most often present on the lower legs, they have also been reported on the feet, thighs, buttocks, and even arms (Baselga, 1997). The clinical course may be prolonged; nodules may ulcerate, heal with scarring, and recur (Requena & Yus, 2001). In cases associated with tuberculosis, there may be signs of pulmonary infection, radiographic evidence of active disease, positive purified protein derivative skin test, or positive interferon gamma release assay (Bolognia et al., 2012).

The histopathology has classically been described as a mostly lobular panniculitis but can reveal a mixed septal and lobular panniculitis as well (Requena & Yus, 2001). The inflammatory infiltrate may include neutrophils, lymphocytes, macrophages, and giant cells (Baselga, 1997). There can be a component of a caseous or coagulative necrosis (Requena & Yus, 2001). Vasculitis is usually seen, but its inclusion as a diagnostic criteria of erythema induratum is contentious (Schneider et al., 1995). The nature of the vessel involved varies from large septal arteries and veins to small venules of the fat lobules (Segura, Pujol, & Trinidade, 2008) (Figure 4).

FIGURE 4. Hematoxylin and Eosin stain, original magnification of 100. Vasculitis involving the small venules of fat lobules.

The differential diagnosis includes erythema nodosum, although the nodules tend to be on the anterior lower legs and resolve sooner. Other entities in the differential include tertiary syphilis (syphilitic gumma), polyarteritis nodosa, and other infectious and inflammatory panniculitis. Histologically, pernio may appear similar to erythema induratum but can usually be ruled out based on clinical history (Requena & Yus, 2001).

Treatment is directed at the underlying cause, such as isoniazid for cases associated with tuberculosis. Other therapies used for the nodules include corticosteroids, nonsteroidal anti-inflammatory drugs, potassium iodide, tetracycline, gold, and mycophenolate mofetil. Supportive measures include rest, compression stockings, and smoking cessation.

We present this case of erythema induratum as a rarely reported entity, given the low incidence of tuberculosis in the United States. Furthermore, this patient showed some less common features in that the patient is male, although the disease is predominantly seen in women, and the histology revealed a septolobular panniculitis rather than a mainly lobular one. Erythema induratum remains an important consideration in the differential diagnosis of lower extremity nodules.

REFERENCES