Background: There are no studies assesing whether patients with idiopathic anaphylaxis are a heterogenous population.

Objective: A study has been carried out to assess whether clinical and functional differences (mast cell releasability) exist between two sub-types of Idiopathic Anaphylaxis (Generalized Idiopathic Anaphylaxis -IA-G- and Idiopathic Anaphylaxis with Angioedema -IA-A-).

Methods: Patients were selected from the Idiopathic Anaphylaxis (IA) patient population of Hospital General de Albacete (Albacete, Spain) and this data were collected between 1990 and 1995. This series is composed of 81 patients. In the interest of seeing whether an IA classification is warranted between IA-G and IA-A, a logistic regression model was constructed in order to know if differences exist between IA-G and IA-A. To evaluate mast cell releaseability in different groups (IA-G, IA-A, atopic patients, urticaria and healthy subjects) we analysed the log 10 wheal area produced by four consecutive concentrations of codeine (from 90 to 3,3 mg/ ml). In those patients with IA-G, the variable urticaria was controlled, but not in those with IA-A. A parallel line assay was used to study the differences arising among all groups. When the conditions of parallelism and linearity ware not fulfilled, a Hotelling´s T2 test was performed.

Results: In the logistic regression equation total IgE, with an O.R. of 1.006 (95% C.I. 1.001-1.01) favoured the presence of IA-G; whereas the presence of urticaria did not favour the presence of IA-G, with an O.R. of 0.159 (95% C.I. 0.04 – 0.507). IA-G and IA-A patients showed a higher cutaneous reaction to codeine than atopic patients (p=0.005 and p=0.001 respectively). However, IA-G patients had a lower reaction to codeine than those patients with urticaria (p=0.048). No differences were observed among patients with IA-A and patients with urticaria, as was the case between IAA and IA-G patients with respect to cutaneous response to codeine.

Conclusion: Apparently, IA-G patients appear to be closely related to the presence of atopy, while IA-A patients are closely related to the presence of urticaria. Along with other unknown factors, an enhanced mast cell releaseability may explain these episodes of Idiopathic Anaphylaxis among atopic patients.

Key-words: Idiopathic, anaphylaxis, angioedema, generalised, codeine, releasability, atopy, urticaria.