Transcranial Doppler in Adults with Sickle Cell Disease
Transcranial Doppler(TCD)is of established use in primary stroke prevention in children with Sickle Cell Disease(SCD)but its value in adults with SCD is unproven. A pilot study to estimate prevalence of high velocity in adults and to correlate findings with those from children with SCD was performed. Thirty three patients with SCD over 18 year of age were studied with TCD using Nicolet TC-2000 during an outpatient visit. There were 3 patients with a remote history of stroke but none were on chronic transfusion. Twenty four(73%)were on hydroxyurea therapy. TCD was performed using the Stroke Prevention in Sickle Cell Disease(STOP)protocol: time averaged maximal mean(TAMM), systolic,and diastolic velocities were recorded for the left and right middle cerebral (MCA) and distal internal carotid artery (ICA). Classification as to normal (TAMM <170 cm/sec), conditional (TAMM 170–199), or abnormal (TAMM >200 cm/sec) was made using the STOP criteria. The mean age was 32 + 8 years (range 18–53). There were 13 men and 20 women. The results were: 19 normal (58%), 1 conditional (3%), 0 abnormal and 13 inadequate (39%). For those with adequate exams (n=21), the average highest TAMM on either side was 111 + 29 cm/sec. Two of four patients with a history of stroke had inadequate exams which may represent occluded vessels but the other two had normal exams. The results are at variance with those reported from children with SCD in that mean velocity is lower and the rate of inadequate exams is much higher(39 vs 5%). In 12 of 13 cases the reason for inadequate studies was no window on one or both sides rather than no MCA recorded. A typical sample of children with SCD would have included 8 cases with TAMM > 170 cm/sec instead of the single case observed in this study. Further study will be needed to determine if the apparent absence of high velocity in adults represents the effects of hydroxyurea, which increases hct by about 15%, is due to cases with unrecognized occlusion or severe stenosis which could also cause low velocity, or indicates that most patients with abnormal TCD as children either have stroke or resolve as they mature. The standards for abnormality based on the STOP study may have to be modified for adults.