Collapsing glomerulopathy associated with natural killer cell leukemia: a case report and review of the literature.

We report a case of collapsing glomerulopathy associated with natural killer cell leukemia in a previously healthy 27-year-old African American man. An initial kidney biopsy showed findings concordant with the cellular variant of focal segmental glomerulosclerosis. A repeated biopsy 3 months later showed collapsing glomerulopathy, likely representing a morphologic evolution from a cellular variant into the collapsing glomerulopathy variant of focal segmental glomerulosclerosis. Collapsing glomerulopathy has been described in connection with a number of disparate disorders in which podocyte injury seems to be the common denominator. The close temporal association between clinical presentation and the development of nephropathy provides support for a direct pathogenic link between the underlying lymphoproliferative disorder and the glomerular lesions. We hypothesize that dysregulated cytokine production by the neoplastic cells led to podocyte alterations and eventually to the development of collapsing glomerulopathy.