Nongranulomatous involvement of the bone marrow in lepromatous leprosy.

Bone marrow involvement in lepromatous leprosy has been characterized histologically by a proliferation of foamy histiocytes containing lepra bacilli, the so-called Virchow cells. The authors have studied three patients with biopsy-proven lepromatous leprosy in whom Fite stain, performed on histologic sections of bone marrow aspirates, demonstrated numerous bacilli lying free in the interstitium in the absence of Virchow cells or focal collections of foamy macrophages. Two of the patients had a recent diagnosis of lepromatous leprosy by skin biopsy; the third patient had a 33-year history of lepromatous leprosy that had been treated. Bone marrow aspirates were performed in all three patients for evaluation of anemia. The findings indicate that the bone marrow may act as a reservoir for viable organisms in the absence of a host response in treated and untreated patients with lepromatous leprosy. The persistence of viable organisms in the bone marrow in patients with lepromatous leprosy may account for the high rate of relapse and/or recrudescence of the disease following cessation of specific therapy. Bone marrow examination with the Fite modification of the acid-fast stain is therefore indicated in such patients to evaluate bone marrow involvement and the efficacy of treatment.