The Use Of Transcranial Doppler Ultrasonography In Adult Patients With Sickle Cell Disease: A Retrospective Analysis

Unlike in children, Transcranial Doppler Ultrasound (TCD) can not currently be used to predict stroke risk in adults with Sickle Cell Disease, and this is confounded by an age related decline in TCD and lack of an established normal TCD velocity range for adults. In addition abnormalities in the extracranial circulation have been associated with increased incidence of stroke in children with SCD, but this has not been shown in adults.

To retrospectively review TCD and carotid duplex ultrasound results from adults with SCD and to correlate with neurological outcome.

TCD and carotid duplex data were collected from 112 patients from January 2003 to December 2012 and analysed retrospectively. Imaging and non-imaging TCD and carotid duplex were performed as a routine out-patient investigation as part of an annual review in the comprehensive adult sickle cell clinic in our unit. STOP velocity criteria were used for stroke risk stratification. Carotid disease was defined as non-significant (<50%), moderate stenosis (50-69%) and severe disease (≥70%).

The mean age of patients was 35.4 (range 17-79) years; 65% were female and 78% had HbSS. There were 5 patient exclusions based on the TCD findings; two were non-diagnostic and three had abnormal scans as part of childhood screening. The remaining 107 patients were divided into two groups; Group I patients had a normal neurological examination (n = 95) and Group II had an abnormal neurological examination with a clinical diagnosis of stroke that preceded TCD/carotid duplex examination (n = 12).

In Group I there were 4 abnormal TCD scans according to STOP criteria; two showed significant asymmetry (>25%) and two showed abnormally low velocities (<50cm/s), one of whom subsequently developed a silent stroke. Although the remaining 91 patients had normal TCD findings; a limited TCD examination was noted in 6 patients and asymmetrical velocities that fell below the 25% threshold were observed in 7 patients, one of whom subsequently developed a symptomatic lacunar infarct. A further eight patients showed extracranial (ICA) disease and one of these also had evidence of a silent stroke on MRI. In Group II, 5 patients showed abnormal TCD findings; four had low velocities (<50cm/sec) and one had low velocities and significant asymmetry. Six patients had severe extracranial ICA stenosis or occlusion on carotid duplex.

There was a significant increase in the incidence of abnormal TCD (C²=19.4, p<0.001) and duplex findings (C²=16.2, p<0.001) in patients in Group II compared to Group I.

Routine screening of adults with SCD using TCD did not show any asymptomatic patients with elevated TCD flow-velocities (>170cm/s), confirming previous studies. However, other abnormal ultrasound findings were observed including; abnormally low or asymmetric TCD velocities and extracranial ICA disease. These abnormalities were associated with stroke in three cases; TCD asymmetry preceded a lacunar infarct by five years, abnormally low velocities preceded a silent infarct by two years and severe extracranial ICA stenosis was associated with a silent infarct. There was a significantly increased incidence of abnormal ultrasound findings in patients who had neurological symptoms (91.6% versus 12.6%). Further investigation of the incidence and implications of abnormal TCD and extracranial carotid duplex findings in adults with sickle cell disease is required. Longitudinal follow-up of patients with low or asymmetric velocities and ICA disease will clarify if these abnormalities are associated with increased neurological morbidity; if so, intervention may be justified. The traditional STOP criteria of raised TCD velocities are inadequate in the adult sickle population, new velocity criteria are required to stratify the risk of stroke in this population.

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