Erythema necroticans exhibiting transepidermal migration of lepra bacilli as a probable source of infection to other family members

infection to other family members A 40-year-old Indian man presented with recurrent crops of painful, ulcerative skin lesions mainly over the extremities and trunk for the last six months. It was associated with high-grade, intermittent fever, myalgia, and polyarthralgia. There were multiple, tender, ulcerated nodules and indurated plaques, many of them exhibiting seropurulent exudation. Nodular infiltrations over both pinna were also present (Fig. 1). Both the hands were mildly swollen and tender. The sensation was slightly diminished bilaterally and symmetrically in his hands and feet. Both of his ulnar nerves and median nerves were grossly thickened and tender. Apart from fever, systemic examination was non-contributory. Ocular and other mucosal examination was normal. Gram staining and bacterial culture of the swabs taken from the exudative ulcerative lesions were non-contributory. Ziehl–Neelsen stain of smear prepared from the seropurulent fluid revealed presence of acid-fast bacilli. A slit skin smear also showed acid-fast bacilli (bacteriological index 5+). A complete hemogram showed neutrophilia with raised erythrocyte sedimentation rate. C reactive protein level was also raised. Biochemical panels and routine urine examination was normal. Incisional biopsies were taken both from a plaque without any ulceration and also from the indurated areas of an ulcerated plaque. Histopathological examination of both the biopsy specimens (Figs. 2 and 3) showed similar features of flat epidermis, upper dermal edema with scattered cellular infiltrate comprising of polymorphs and lymphocytes, perineural and peri-appendageal granulomatous inflammation (comprising of lymphocytes, epithelioid cells, neutrophils, and foam cells), and lobular panniculitis (comprising of mononuclear cells, histiocytes, neutrophils, and eosinophils), and features of small vessel vasculitis in the dermis and subcutaneous tissue. Fite stain (Fig. 4) demonstrated clumps of predominantly solid staining and a few fragmented and granular acid-fast bacilli in the subcutaneous tissue, dermis, and epidermis. One noteworthy finding was the presence of numerous lepra bacilli (both intracellular and extracellular) in the malpighian layer and stratum corneum suggestive of their transepidermal migration. Based on the clinical and histopathological features, a diagnosis of erythema necroticans was made. We started multidrug therapy for leprosy as recommended by World Health Organization along with a course of prednisolone, started as 40 mg/day and gradually tapered over a period of three months. Within a couple of months, the skin lesions almost completely healed. After six months of the initial presentation of the patient to us, his elder son and mother presented with hypopigmented anesthetic patches, which were further confirmed clinically and histopathologically as borderline tuberculoid leprosy. Erythema nodosum leprosum, the main presenting feature of a type-2 reaction in leprosy, may complicate the course of borderline lepromatous or lepromatous leprosy. Severe erythema nodosum leprosum may become vesicular or bullous and may eventually break down, which is termed as erythema nodosum necroticans or erythema