[Urticaria pigmentosa--an obligate systemic disease? Results of nuclear medicine studies and etiopathogenetic significance].

The objective of the present investigation was to establish the frequency of systemic spreading of urticaria pigmentosa by means of bone and bone marrow scintigraphy as a noninvasive imaging technique with a low radiation exposure. Bone scintigraphy: Seven of nine patients investigated showed diffuse and focal nuclide accumulation. After exclusion of other causes by reference to the case history and the clinical and chemical laboratory findings, these nuclide accumulations were regarded as mastocytosis-specific in accordance with the atypical localization. Bone-marrow scintigraphy: All the patient investigated showed a peripheral expansion of the bone marrow. This must be interpreted as an expansion of the macrophages of the bone marrow on the basis of the method used. Since the mast cell is regarded as a more highly differentiated form of the same cell-type as macrophages/monocytes, on the basis of the scintigraphic results presented, urticaria pigmentosa can be regarded pathogenetically as a hyperplasia of the macrophages of the bone marrow organ, with increased differentiation in mast cells. The extent of this differentiation and its pathological quality then determine the clinical signs and symptoms (cutaneous, systemic, or malignant mastocytosis). Urticaria pigmentosa thus has the character of a systemic disease.