Understanding cutaneous tuberculosis in children

Tuberculosis continues to remain a major public health problem in developing nations. India has the highest burden of tuberculosis in the world, with the World Health Organization estimating its incidence in India to be about 2.1 million for the year 2013, accounting for a little over one-fifth of the global incidence. Prevalence of cutaneous tuberculosis in the pediatric population varies geographically in India, ranging from 18% to 54% of all skin tuberculosis. In recent times, a steadily rising trend in the number of childhood and adolescent cutaneous tuberculosis cases has been noticed in north India, up from 63 cases over a period of 7 years from 1968–1999 and 103 cases in far shorter time-spans of 15 and 18 months in 2004 and 2007, respectively. Cutaneous tuberculosis may behave differently in children, as compared to adults. In this article, we highlight the peculiarities of cutaneous tuberculosis in children and discuss the reasons behind the same. The common morphological variants of cutaneous tuberculosis and its sites of predilection are known to differ between children and adults. Unlike adults where lupus vulgaris is the commonest form, scrofuloderma is seen more commonly in children. Kumar et al. attributed this discrepancy to the habit of consuming unboiled/unpasteurized milk prevalent in many parts of India, which may lead to infection of cervical lymph nodes via tonsils by Mycobacterium bovis. Lupus vulgaris is seen frequently over the head/neck region in adults. This is in contrast to children, where buttocks and legs are more commonly affected and could be explained by the direct inoculation of mycobacteria on their exposed body parts, as they play without clothing and defecate in the open. Lesions at these sites can even extend to the genitals, which may have a negative impact on their sexual health later on. Disfiguring scars on the vulva have been described due to lupus vulgaris. Even the unusual presentations of cutaneous tuberculosis are more frequent in children than adults. Sporotrichoid spread of lupus vulgaris and scrofuloderma have been reported in children. A good lymphatic drainage coupled with increased risk of injury due to increased physical activities in this age group may explain the propensity of this rare clinical presentation in the pediatric population. “Inverse sporotrichoid” pattern, which refers to linear arrangement of lesions on proximal lower extremities, has also been described in children for tuberculosis verrucosa cutis and gummas, possibly resulting from retrograde spread of infection from the inguinal lymph nodes. Coexistence of more than one variant is not uncommon (Fig. 1). Often, children present with extensive or disseminated disease. Multifocal involvement of cervical, axillary, and inguinal lymph nodes and bilaterally symmetrical scrofuloderma affecting both the feet have been reported. Disseminated gummatous lesions can be seen in undernourished children (Fig. 2). Lesions may be localized to one site initially but spread aggressively over time. Systemic involvement is also seen more in children. Various authors have found the prevalence of underlying visceral involvement to vary from 12.7% to 53.4%, much more than the 13% reported in adults. 6,10 Lungs, bones, and abdomen are commonly involved. What causes cutaneous tuberculosis to be more severe in children? One logical explanation would be impairment of the immune response in the younger age group. It is possible that