[Immunodeficiency in adult patients as the first sign of a primary underlying condition].

Three male patients, aged 56, 40 and 52 years, presented with recurrent infections and clinically suspected immunodeficiency, which was confirmed by the presence of hypogammaglobulinaemia. In one patient, no obvious underlying disease was identifiable, and primary immunodeficiency syndromes were considered in the differential diagnosis. A thorough diagnostic work-up revealed the presence of non-Hodgkin lymphoma in an iliac crest biopsy specimen. The second patient was found to have a thymoma. In the third patient, the immunodeficiency was the key to the ultimate diagnosis of multiple myeloma, which was still asymptomatic at that stage. Establishing the underlying condition had important therapeutic and prognostic consequences in these patients.