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The disorders of xanthohistiocytic proliferation involving histiocytes, foam cells, and mixed inflammatory cells are divided into Langerhans cell histiocytosis (LCH) and non-Langerhans cell histiocytosis (non-LCH).

Langerhans Cell Histiocytosis (Histiocytosis X)

LCH is an idiopathic spectrum of disorders characterized by a clonal proliferation of Langerhans cells. Clinically, LCH is characterized by lytic bony lesions and cutaneous findings that range from soft tissue swelling to eczema- and seborrheic dermatitis-like skin changes and ulceration.

Insight

Histiocytosis can be extremely difficult to diagnose. In infants with diaper rash that will not heal, particularly if there are erosions in the folds or petechiae/purpura, histiocytosis should be considered.

Synonyms Class I histiocytosis, nonlipid reticuloendotheliosis, eosinophilic granulomatosis.

Classification

LCH has four overlapping forms:

  1. 1. Letterer–Siwe disease: aggressive LCH with diffuse skin and organ infiltration and thrombocytopenia

    2. Hand-Schüller-Christian disease: LCH with lytic skull lesions, exophthalmos, and diabetes insipidus

    3. Eosinophilic granuloma: single osteolytic bony lesion ± skin/soft tissue lesion

    4. Hashimoto–Pritzker disease: congenital self-healing reticulohistiocytosis

Epidemiology

Age Any age, common 1 to 3 years.

Gender M > F, 2:1.

Incidence Rare, 5/million children.

Genetics Familial case reports.

Pathophysiology

The proliferating Langerhans cell appears to be primarily responsible for the clinical manifestation of LCH. The stimulus for the proliferation may be a disturbance of intracellular lipid metabolism, a reactive response to infection (?viral), a primary immunologic disorder of the host, or an inherited neoplastic disorder.

History

LCH has a broad clinical spectrum, but in the most aggressive form (Letterer–Siwe disease), the infant appears systemically ill with a generalized skin eruption (seborrhea, petechiae, and purpura) followed by fever, anemia, thrombocytopenia, adenopathy, hepatosplenomegaly, and/or skeletal lesions.

Physical Examination

Skin Findings

Type Papules, plaques, vesicles, scale, petechiae, purpura, ulceration, necrosis.

Color Pink, flesh-colored.

Size 1 to 2 mm.

Distribution Flexural areas: neck, axillae (Fig. 19-1), and perineum > trunk (Fig. 19-2).

FIGURE 19-1

Histiocytosis X Erythematous plaques with ulceration and maceration in the axilla of an infant.

FIGURE 19-2

Langerhans cell histiocytosis Erythematous papules and a crusted, purpuric plaque on the abdomen of an infant.

General Findings

Fever Lymphadenopathy (LAD). Ill appearance.

Pulmonary Infiltrate disease of the lung bases and midzones, pneumothorax.

Liver Hepatosplenomegaly.

Bone Osteolytic lesions: calvarium, sphenoid bone, sella turcica, mandible, long bones of upper extremities (UEs), vertebrae.

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