The urinary excretion of
histamine and its main metabolite,
1-methyl-4-imidazoleacetic acid (MeImAA), was determined in 30 adult patients with the clinical diagnosis of
urticaria pigmentosa (UP). Clinical and laboratory investigations including skin histology, bone marrow examination, and scintigraphy of the skeleton, liver, and spleen revealed systemic manifestations in 14 cases. Among the 16 cases with dermal proliferation of mast cells only 3 cases classified as
telangiectasia macularis eruptiva perstans (TMEP). All patients with
systemic mastocytosis and UP excreted increased amounts of MeImAA in the urine while normal amounts were found in 2 of the patients with TMEP. A significant correlation existed between MeImAA excretion and the extent of mast cell infiltration in skin and internal organs. No such correlation was found for urinary
histamine. Urinary MeImAA but not
histamine is therefore considered a useful
indicator of systemic involvement by reflecting the size of the mast cell
histamine pool. The main symptom of the patients was
pruritus, which was moderate to severe in 17 and mild or absent in 13 cases. Gastrointestinal symptoms were present in 14 patients. However, there was no obvious correlation between the excretion of MeImAA and any of the symptoms recorded. Neither was the severity of
pruritus correlated to the
histamine content of the skin, which was measured in both lesional and unaffected skin in 23 of the patients. Thus, symptoms possibly caused by
histamine in
mastocytosis patients are not directly related to urinary
histamine metabolite excretion or tissue
histamine content.