Idiopathic Secondary Post-Transplant Thrombocytopenia (ISPT) Following Autologous Hematopoietic Progenitor Cell Transplantation (HPCT) is Associated with Transplantation of Lower Numbers of Primitive Hematopoietic Progenitors

Background: Platelet counts often drop after initial hematopoietic engraftment. We hypothesized that secondary thrombocytopenia is related to the stem cell content of the graft. Methods: We performed a retrospective analysis of 323 consecutive patients who underwent autologous blood (97%) or BM (3%) HPCT between 2000 and 2005 for Hodgkin’s lymphoma (n = 53), NHL (n = 85), multiple myeloma (n = 166), acute leukemia (n = 16), and solid tumor (n = 5). ISPT was defined as a >50% decline in blood platelets following initial engraftment to a value less than 100 K/mcL, in the absence of infection or relapse, in the first 100 days post-transplant. Engraftment, transfusions, infections, relapse, and survival were recorded with a median follow-up of 410 days. Results: 303 patients were evaluable and achieved a transfusion-independent platelet count of >20K/mcL, at a median of 17 days post-transplant. The maximal platelet count was a median of 192 K/mcL and occurred on a median of 22 days. Sixty-three patients (21%) had secondary thrombocytopenia after initial engraftment, with 3 cases of relapse and 11 cases of sepsis, leaving 49 patients (15%) with ISPT, and 254 controls. Patients with ISPT engrafted at a median of 17 days, with a maximal platelet count of 162 K/mcL on day 19. Platelet counts in ISPT patients dropped to a nadir of 34 K/mCL (range 4 K–98 K/mcL) on day 35 with subsequent recovery to a median of 148 K/mcL on day 71. Mean CD34+ cells/kg transplanted in ISPT patients (9 ± 7 × 10E6/kg) were similar to cell doses transplanted in controls (11 ± 14 × 10E6/kg), but IPST patients received fewer CD34+CD38− HPC (0.08 ± 0.08 × 10E6/kg) versus controls (0.13 ± 0.24 × 10E6/kg, P = .005, 2 sided T-test). HIT and anti-platelet antibodies were absent, and only 16% of BM biopsies in patients with ISPT had increased megakaryocytes. Fourteen of forty-nine patients with ISPT received steroids and/or IVIG and had similar platelet recoveries to those not treated. Lymphoma patients and recipients of busulfan conditioning regimens were over-represented in patients with ISPT compared to controls (P < .001). Three-year actuarial survival was not significantly different between the 49 ISPT cases (79%) versus the 254 controls (76%). Conclusions: ISPT occurring within the first 100 days after autologous HPCT is common, and associated with transplantation of lower numbers of phenotypically primitive HPC. IPST does not appear to be an auto-immune phenomenon, is self-limited, and is not associated with adverse long-term survival (Table1).Table 1Comparison of IPST Cases vs ControlsAge (years)Gender (male)HL and NHL*Pre-trx XRTMedian day Plt engraftedBM cellularity day 40–45Platelet transfusion incrementIPST N = 4948 years55%73%4%17 days35%32K/mcLControls N = 25451 years63%36%7%17.5 days34%31K/mcL*P < .001 Open table in a new tab *P < .001