COMMENTARIES

Diagnosis of Intracranial Atherosclerosis

Edward Feldmann, M.D.1 and Aevan Mclaughlin, B.S. 2, 1Professor of Clinical Neurosciences, Warren Alpert School of Medicine, Brown University, Providence, RI and 2Neuroscience, Dickinson College, 158 Bear Hill Road #405,
Cumberland, RI 02864

Intracranial atherosclerosis is a major cause of ischemic stroke in the United States, estimated to be responsible for over 70,000 strokes each year [1,2], and is considered a major cause of stroke worldwide. Patients with intracranial atherosclerosis have a high risk of recurrent stroke. Despite antithrombotic therapy, symptomatic patients with > 50% stenosis have an 11% risk of having a recurrent stroke in the territory of the stenotic artery at one year, and patients with ≥ 70% stenosis have a risk as high as 23% for stroke at one year [3].    

          Catheter angiography is the gold standard for the diagnosis of intracranial atherosclerosis, but it is associated with a significant risk of stroke [4]. Noninvasive diagnostic tests such as magnetic resonance angiography (MRA), transcranial Doppler (TCD), and computed tomography angiography (CTA), are being used with increasing frequency for diagnosing intracranial atherosclerosis. These tests have the benefit of being cheaper and safer for the patients. However, they may not be adequate to replace catheter angiography.

          The Stroke Outcomes and Neuroimaging of Intracranial Atherosclerosis (SONIA) trial found that MRA, TCD, and CTA perform better to exclude the presence of atherosclerosis than to detect it [5]. Therefore, these noninvasive tests need confirmation by angiography for an abnormal test result.

          It is also important to note that the performance of the noninvasive tests depends on the prevalence of the disease in the population. Figure 1 shows why the positive predictive value of the noninvasive test is proportional to the prevalence of disease.

 

Figure 1.

prevalence*sensitivity

PPV =  ___________________________________________________________________________________
prevalence*sensitivity + (1-specifity)*(1-prevalence)

 

Therefore, these noninvasive tests would perform differently in an Asian population, since the prevalence of intracranial stenosis is so much greater [6,7].

          Currently, there are few multi-center, prospective trials assessing the performance of these diagnostic tests. Due to rapidly increasing technology and lack of funding, there has been a paucity of research regarding the performance of diagnosis tests. The lack of research leaves physicians with inadequate information on these tests.

          There is currently no specific treatment for intracranial atherosclerosis. Antithrombotic therapy, statins, and reduction of modifiable risk factors are standard for the prevention of secondary stroke [8]. Other possible treatments are angioplasty with or without stenting, which have shown promise but need to be investigated further. The National Institute for Neurological Disorders and Stroke (NINDS) recently funded a grant, Stenting and Aggressive Medical Management for Preventing Recurrent Stroke in Intracranial Stenosis (SAMMPRIS) trial, which would provide further information on the best medical treatment and determine a role for stenting for intracranial stenosis.

          Intracranial atherosclerosis should be diagnosed using noninvasive tests first. These tests reliably exclude disease in a patient. However, if the result of the noninvasive tests shows disease, then the diagnosis should be confirmed by catheter angiography. If angiography confirms intracranial atherosclerosis, then aggressive medical therapy should be started. Stenting should be considered for arteries with stenosis greater than 70%, in patients who do not respond to medical therapy. Stenting is still an investigational treatment. However, patients with ≥ 70% stenosis are at a particularly high risk of recurrent stroke and are potential candidates for this treatment [3].

          There is an obvious need for more research regarding the diagnosis and treatment of intracranial atherosclerosis. However, the outlook for these patients is improving. There is better technology for diagnostic tests, a better understanding of the functional role of these tests, and better treatment options for patients with intracranial atherosclerosis.

 

References

  1.    Wityk R, et al. Race and sex differences in the distribution of cerebral atherosclerosis. Stroke 1996;27(11):1974-80.
  2.    Williams GR, et al. Incidence and occurrence of total (first-ever and recurrent) stroke. Stroke 1999;30:2523-28.
  3.    Kasner SE, et al. Predictors of ischemic stroke in the territory of a symptomatic intracranial arterial stenosis. Circulation 2006;113:555-63.
  4.    Dion J, et al. Clinical events following neuroangiography: A prospective study. Stroke 1987;18:997-1004.
  5.    Feldmann E, et al. The Stroke Outcomes and Neuroimaging of Intracranial Atherosclerosis (SONIA) trial. Neurology 2007;68:1-7.
  6.    Sacco RL, et al. Race-Ethnicity and determinants of intracranial atherosclerotic cerebral infarction: The Northern Manhattan Stroke Study. Stroke 1995;26(1):14-20.
  7.    Feldmann E, et al. Chinese-white differences in the distribution of occlusive cerebrovascular disease. Neurology 1990;40(10):1540-45.
  8.    Sacco RL, et al. Guidelines for prevention of stroke in patients with ischemic stroke or transient ischemic attack: A statement for healthcare professionals from the American Heart Association/ American Stroke Association Council on Stroke: Co-sponsored by the Council on Cardiovascular Radiology and Intervention: The American Academy of Neurology affirms the value of this guideline. Circulation 2006;113(10):e409-49.

 

 

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