Severe combined immunodeficiency disease: a pathological analysis of 26 cases.

Autopsy material and clinical information were analyzed in 25 cases of untreated or unsuccessfully treated severe combined immunodeficiency disease and one case successfully treated by bone marrow grafting. Two cases were adenosine deaminase deficient and one was nucleoside phosphorylase deficient. The histological appearance of the thymus fell into four clearly recognizable patterns: simple dysplasia, dysplasia with corticomedullary differentiation, dysplasia with pseudoglandular appearance, and atrophic pattern. Three cases lacked lymph nodes and belonged to the category of thymic dysplasia with pseudoglandular appearance. From the data, the following conclusions can be made: (i) The thymic atrophic pattern is a phase in a dynamic process of which the end result is simple dysplasia or dysplasia with corticomedullary differentiation. (ii) The pseudoglandular pattern represents a disease process of early intrauterine onset. (iii) At least a proportion of the cases represent a T-cell defect rather than a lymphoid stem-cell defect. (iv) The lymphoid germinal centers are not the source of plasma cells. (v) The graft-versus-host reaction probably causes lymphoid cells depletion in lymph nodes and spleen.