Detecting leptomeningeal spread of AML
Conditioning procedures prior allogeneic stem cell transplantation aim on the eradication of all malignant cells as the prerequisite for cure. However many drugs used for conditioning do not reach all anatomical compartments, since these are separated by a special structure and are therefore called “sanctuary sites”. This is particularly true for the central nervous system (CNS), which is protected by a membrane that prevents a sufficient penetration of several chemotherapeutical agents into the cerebrospinal fluid (CSF). Patients with a high risk of CNS disease involvement are therefore often conditioned by total body irradiation (TBI) prior to SCT, which effectively treats the CNS . Since most of the patients in the last 20 years received a standard conditioning with either TBI or busulfan, which also reaches high concentrations in the CNS, the probability of developing CNS related relapse after SCT was considered to be low. Consequently, therefore a large recent EBMT survey did not emphasize on CSF analysis and intrathecal prophylaxis prior to allogeneic transplant . However, especially the indications for allogeneic SCT have changed during the last decade in means that more patients with refractory disease are treated [3,8]. Additionally more patients are conditioned with a reduced-intensity regimen reducing the efficacy of CNS targeted treatment.
At our institution routinely an examination of the cerebrospinal fluid in every patient receiving an allogeneic transplant suffering from acute myeloid leukaemia is performed. In the present study we retrospectively evaluated the cytological results of 204 patients, who received an allogeneic stem cell transplant within the decade from 1996 to 2009. 2-3 ml of CSF were collected by lumbar puncture and evaluated by cell counting and a cytological analysis. Cell count was performed by diluting 20 µl of CSF with trypan blue stain according to the expected cell count. The suspension was transferred into a Neubauer modified chamber, the 4 edge squares were analysed and the viable cells were counted using a 40x high power microscopy. For the microscopic analysis CSF was diluted to an expected cell count of 50 – 100 cells/µl. 200 µl of cell suspension are transferred into a Shandon cytospin device (GMI, Inc, Ramsey, Minnesota). Centrifugation was performed at 1500 rpm and low acceleration for 5 minutes. Films were dried and stained with may-gruenwald-giemsa. We performed only conventional morphological analysis, no routine immuno–staining.
Image presenting CSF cytopspin from a patient with AML. Cell count was 3/µl. Note the large blasts with fine cytoplasmatic granula.
Out of the 204 patients 17 patients showed myeloid blasts in the CSF prior to transplantation, corresponding to a percentage of 8%. This frequency is in line with another study in adult AML patients which showed also a CNS involvement in about 5% of patients  and higher than in the series published by an Italian group . Cell counts at the timepoint of diagnosis ranged from normal to 499 cells per µl CSF. We observed CNS involvement in eight patients with CSF cell counts less than or equal 3 cells per µl. In these patients involvement could only be detected by careful morphological CSF examination. Only nine patients had a history of CNS-involvement or had clinical symptoms suspicious for leptomeningeal disease. All patients underwent a compartment directed approach with repeated courses of intrathecal chemotherapy (MTX, MTX in combination with cytosine-arabinoside, or liposomal cytosine-arabinoside) sequentially combined to their regular conditioning regimen. Intrathecal treatment was continued until the clearance of blasts was confirmed by two sequential CSF analyses.
Only two patients with CNS involvement are still alive and the median survival is short, with most patients dying from non-relapse mortality. This is consistent to other studies showing a bad prognosis in adult patients with CNS involvement . We conclude, that CNS involvement is a relatively rare, however considerable event in often asymptomatic patients with AML prior to stem cell transplantation. Affected are especially patients, who are not in remission at the time of transplant. Furthermore we learned that normal cell counts in the CSF do not exclude CNS involvement because blasts may become only detectable after centrifugation of the CSF.
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