Metabolism of histamine in myotonic dystrophy a dual pattern of inactivation of intestinal histamine.

The catabolism of orally and subcutaneously administered 14C histamine was studied in myotonic dystrophy patients. No definite abnormalities were observed as for subcutaneously administered histamine. The catabolism of orally administered histamine followed two distinct patterns: In patients with a relatively low endogenous urinary conjugated histamine excretion at the time of testing, small quantities of radioactivity were excreted in the stools (mean 0.25 per cent), whereas the quantity of exhaled 14CO2 was in the control range (mean 14.4 per cent), and the exhalation curve diphasic as in controls. In patients with a relatively high urinary conjugated histamine excretion, the catabolic pattern differed: There was a relatively high faecal excretion of radioactivity (mean 20.1 per cent), whereas the exhalation of 14CO2 was markedly reduced (i.e. mean 0.5 per cent, versus a mean control level of 8.9 per cent). Diphasicity of the exhalation curve was not present in these patients. It has previously been demonstrated that a patient with myotonic dystrophy may shift between being a normal and a high conjugated histamine excretor. It is thus possible that all patients with myotonic dystrophy may pass through phases with abnormal catabolism of intestinal histamine.