Background: There has been a long controversy about the tuberculous cause of erythema induratum, a chronic form of nodular vasculitis.
Method: We investigated clinical, histopathologic, and immunohistochemical features of patients with erythema induratum who showed positive tuberculin hypersensitivity reactions or had associated active tuberculosis.
Results: The ages of the 32 patients (M 7: W 25) ranged from 13 to 66 years (mean 36.6 years). All patients displayed recurrent crops of tender, painful, violaceous nodules or plaques. Most lesions presented on the legs, but they also occurred on thighs, feet, buttocks, and forearms. The skin lesions evolved for several weeks and healed with scarring and residual pigmentation. Twenty-two patients were treated with isoniazid alone and the remaining 10 patients received combinations of antituberculous drugs. Relapses were encountered in four patients who received isoniazid alone or stopped the medication against medical advice. In most biopsies, histologic examination revealed lobular or septolobular panniculitis with varying combinations of granulomatous inflammation, primary vasculitis, and necrosis. Immunohistochemical labeling revealed a preponderance of T lymphocytes, monocyte-macrophages, and Langerhans' cells, indicative of a type IV hypersensitivity reaction.
Conclusion: Erythema induratum of Bazin has distinct clinical, histopathologic, and immunohistochemical features. Erythema induratum of Bazin should be considered as a separate entity of nodular vasculitis caused by latent foci of tuberculous infection.