9. Patients on full-dose anticoagulants (e.g., warfarin) with PT international normalized ratio (INR) >1.5 are eligible provided that: 1. Patients are receiving anticoagulation (warfarin or low molecular weight heparins (LMWH)) only if the patients can be off of warfarin for 4-5 days prior to the LP and placed on LMWH in that interim, and if the 'treatment dose' of LMWH can be safely held for 24 hours before and after the LP.