Immunological studies were performed on 4 elderly diabetic patients with Malignant External Otitis caused by Pseudomonas aeruginosa. Impairment of cellular immunity was found. Skin tests for delayed hyper-sensitivity to PPD, SK-SD and Mumps antigen were negative and stimulation rates of peripheral blood lymphocytes by PHA, Con-A and PWM were depressed in all 4 patients. Serum immunoglobulins and complement levels were normal exept in one case in which para-protein IgG was found. Peripheral blood lymphoid cell markers and the neutrophil nitroblue tetrazolium (NBT) test were within normal limits in the 2 patients tested. These results indicate that cellular immune deficiency predisposes to the development of Malignant External Otitis in elderly diabetic patients.
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