Thursday, January 6, 2011
The physical exam in the MRI age
In busy spine clinics, it is common practice to review MRIs or MRI reports prior to seeing patients in order to focus one’s history and physical exam and maximize efficiency. While this may seem to improve efficiency, it could also bias one’s findings from the interview and exam and could detract from the value of these crucial parts of the diagnostic process. In the January 1 issue, Suri and colleagues evaluated the test characteristics of common physical exam tests for the diagnosis of midlumbar (L2-4) versus low lumbar (L5 or S1) nerve root impingement as well as for impingement at the specific root level. Importantly, they only included patients in the study if they did not have an MRI available for review at the time of physical exam, to prevent the possibility of bias in their exam findings. They found that a positive femoral stretch test, decreased medial ankle sensation, and a diminished patella reflex all significantly increased the likelihood of midlumbar nerve root impingement, while a diminished Achilles reflex increased the likelihood of L5 or S1 impingement. Their individual nerve root findings also helped clarify which tests are specific for individual levels, with diminished anterior thigh sensation increasing the likelihood of L2 impingement, a positive femoral stretch test of L3 impingement, a diminished patella reflex of L4 impingement, and hip abductor weakness of L5 impingement. Since this study included only patients with lower extremity pain and correlated the exam findings to MRI results, it is likely the most useful study of physical exam findings in radiculopathy patients.
How can this study be used clinically? First, it is a good reminder to perform a history and physical prior to reading the imaging studies so that a diagnosis can be made on history and physical and then confirmed with imaging rather than vice versa. Given the high rate of asymptomatic MRI abnormalities, one could easily be misled if the history and physical is biased by knowledge of the imaging findings. Second, this study demonstrates that certain findings can reliably localize findings to the midlumbar versus low lumbar region. If certain physical exam tests are positive, the clinician can then confidently review the MRI and either confirm or refute their diagnosis based on the physical exam. What this study also points out is that the absence of physical exam findings does not rule out nerve compression. With the exception of the straight leg raise, no other individual test had a sensitivity of greater than 50%. This implies that for any given test of midlumbar impingement, less than 50% of patients will have a positive test. Not surprisingly, combining the number of tests increases sensitivity, but at the cost of specificity (i.e. increases the false positive rate). The bottom line, which likely supports current clinical practice, is that a positive test helps localize nerve compression, while negative tests do not provide much information.
Please read Dr. Suri’s article and accompanying commentary. Will this article affect your diagnostic algorithm for patients with lumbar radiculopathy? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS