Langerhans cell histiocytosis.

Histiocytosis X, or Langerhans cell histiocytosis (LCH), is a rare disease, with an estimated incidence of 1/200,000 per year in children under 15 years of age. It has a wide clinical spectrum, from single bone involvement (eosinophilic granuloma) to multisystemic disease with organ failure. The treatment of LCH is still controversial. While single system disease may spontaneously recover or requires minimal treatment, some multisystemic disease with organ dysfunction may resist systemic chemotherapy. The mortality rate in this latter subgroup of patients is relatively high and reaches 40% of the cases. A rational approach to the treatment of LCH is based on a better understanding of clinical and pathophysiological features. A prospective multicentre trial including scientific research should be planned, in order to determine the optimal treatment of LCH and to ameliorate the prognosis of the severe unresponsive form of the disease.