Defective monocyte function in pyoderma gangrenosum with IgG kappa paraproteinaemia.

Peripheral blood monocytes from a patient with pyoderma gangrenosum and paraproteinaemia showed defective phagocytosis; longitudinal observations demonstrated an association between the defect, the level of paraprotein and the clinical activity of the pyoderma. Treatment with Melphalan led to a reduction in the paraprotein level and remission of the pyoderma and was accompanied by normalization of monocyte function. After 8 months remission the paraprotein level rose again and was accompanied by a recurrence of the monocyte defect; shortly after this the pyoderma recurred. Pre-incubation of normal monocytes with the patient's plasma or immunoglobulin fractions revealed that a similar defect could be induced in normal cells by the patient's monomeric IgG. The patient's serum also had anti-heparin activity and the relationship between this and the phagocytic defect was explored. These studies indicate a possible pathogenetic mechanism underlying the association between pyoderma gangrenosum and monoclonal gammopathy.