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LANGERHANS CELL HISTIOCYTOSIS AND OTHER

HISTIOCYTOSES

Langerhans cell histiocytosis (histiocytosis X)

This histiocytic disorder (Ch.19) is most frequent in children. It causes a rash that resembles a severe seborrheic rash, with crusted papular lesions, erosions, granulomatous areas, and purpuric areas. The rash may present on the nappy area, trunk, or scalp. Internal involvement may occur, especially diabetes insipidus (in 25–50% with systemic disease), and treatment is usually with radiotherapy or chemotherapy, or both.

     Occasionally, solitary nodular skin lesions known as eosinophilic granuloma of the skin may occur as a rare variant of Langerhans cell histiocytosis (LCH), which may be cured by excision, radiotherapy, or intralesional steroid injection.

Juvenile xanthogranuloma

Juvenile xanthogranuloma (JXG) is much the commonest of the histiocytic disorders. It occurs in children, usually as one or a few yellowish orange papules or nodules, most commonly on the scalp or face(Figs 11.71). As discussed earlier, its yellow color is most likely to be interpreted as a xanthoma, but it also enters the differential diagnosis of mastocytosis. It does not have any significance in most cases, and lesions generally resolve without treatment. However, involvement of the eyes may occur, and there is a rare association between JXG, neurofibromatosis type 1 (NF1), and juvenile myelomonocytic leukemia (although JXG and NF1 can coexist without leukemia also).

Other histiocytoses

Most other histiocytoses are rare. They include types that are the following.

•	Familial—familial sky blue histiocytosis and hereditary progressive mucinous histiocytosis.
•	Eruptive or disseminated—benign cephalic histiocytosis (usually in children), generalized eruptive histiocytosis (mainly in adults), and xanthoma disseminatum (Figs 11.72)
•	Paraneoplastic—diffuse plane xanthomatosis and necrobiotic xanthogranuloma (with paraproteinemia)(Figs 11.73).
•	Usually systemic but occasionally confined to skin—massive sinus histiocytosis (Rosai–Dorfman disease, (Figs 11.74)

Fig. 11.73 Necrobiotic xanthogranuloma is a rare disease, associated with paraproteinemia (usually of IgG type). Lesions are nodules and plaques that may be annular and, due to their yellowish color, may resemble necrobiosis lipoidica. Periorbital involvement is typical, and the lesions may be locally destructive. Early periorbital lesions may be confused with xanthelasma. (Courtesy of Theodore Sebastian, M.D.)

Fig. 11.74 Rosai–Dorfman disease (massive sinus histiocytosis). The skin is involved in a minority of cases, but it may be the dominant or the presenting feature on some occasions. Pigmented plaques and nodules are the typical skin lesion in this rare disorder.

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White/Cox: Diseases of the Skin, 2ed.(c) 2006, Elsevier Inc. All rights reserved.