Nodular tuberculid: a report of four patients.

The tuberculids are hypersensitivity reactions to Mycobacterium tuberculosis (MTB) and include papulonecrotic tuberculid (PNT), lichen scrofulosorum, erythema induratum of Bazin (EIB), and phlebitic tuberculid. Papulonecrotic tuberculid displays papulonecrotic lesions mostly on the extensor surfaces of the limbs. Histopathology shows necrosis, granulomatous inflammation (GI), and occasionally vasculitis, usually in the superficial dermis. Erythema induratum of Bazin shows nodulo-ulcerative lesions on the posterior aspect of the legs. Histopathology reveals a septolobular panniculitis, necrosis, GI, and vasculitis. The Mantoux test is strongly positive and associated tuberculosis (TB) may be present in both conditions. MTB cannot be demonstrated with a Ziehl-Neelsen (ZN) stain or cultured. The polymerase chain reaction has demonstrated MTB DNA in PNT (50%) and EIB (25%). The tuberculids respond to full anti-TB treatment. We document four patients with nodules on the legs in whom the pathologic changes were situated in the deep dermis and adjacent subcutaneous fat. Nodular tuberculid (NT) is regarded as a suitable term for these lesions. All patients were female. Their ages were 19 months, 12 years, 17 years, and 5 years. All patients presented with nodules on the limbs. These nodules were approximately 1 cm in diameter, dull red or bluish-red, and nontender. Ulceration was not present. The number of nodules varied from a few to many. The Mantoux test was strongly positive in all the patients. Associated pulmonary TB was present in two patients. Histopathology showed GI (n = 4), vasculitis (n = 2), and coagulative necrosis (n = 2). A ZN stain was negative in each case. All patients received anti-TB treatment for 6 months [rifampicin (n = 4), isoniazid (n = 4), pyrazinamide (n = 4), and ethambutol (n = 2)]. At 12 months follow-up, skin and pulmonary lesions had resolved in all. Nodular tuberculid should be distinguished from arthropod bites and papular urticaria, dermal erythema multiforme, evolving vasculitis, evolving folliculitis, and erythema nodosum. Histopathologically NT should be distinguished from other causes of granulomatous vasculitis and GI with or without necrosis. In children with nodules on the limbs unresponsive to routine treatment, skin biopsy should be done to exclude NT. Nodular tuberculid represents a hybrid between PNT and EIB with characteristic clinicopathologic features and should be included in the classification of cutaneous TB.