Cervical spondylotic myelopathy (CSM) is a relatively common cause of balance dysfunction and loss of manual dexterity in the middle aged and elderly population. Like many spinal conditions, there is not a gold-standard test available to make the diagnosis. The combination of symptoms (i.e. clumsy hands, off balance), physical exam findings (hyperreflexia, Hoffman's sign, clonus, etc.), and MRI demonstrating cord compression are necessary to make the diagnosis. For patients with severe CSM, the diagnosis is frequently straightforward, though mild or atypical cases can be much harder to diagnose. Given the lack of a gold-standard test, providers would benefit from a better understanding of the test characteristics of factors that go into the diagnosis. To quantify the test characteristics of the physical exam maneuvers that contribute to the diagnosing CSM, Dr. Fogarty and colleagues performed a literature review and meta-analysis on the topic. The only physical exam test with any even moderate quality data regarding test characteristics was the Hoffman sign, so their paper focused on this test. They found three papers including patients referred to a spine surgeon for cervical complaints that reported the sensitivity and specificity of the Hoffman sign, using MRI as the "gold standard" diagnostic tool. The authors combined the 3 studies to yield 201 patients, 46% of whom had an MRI "diagnosis" of myelopathy. Overall, the Hoffman sign had a sensitivity of 59% and specificity of 78%, corresponding to a false negative rate of 41% and a false positive rate of 22%. The positive likelihood ratio (proportion of CSM patients with a positive Hoffman sign divided by non-CSM patients with a positive Hoffman sign) was 2.6 and the negative likelihood ratio (proportion of CSM patients with a negative Hoffman sign divided by non-CSM patients with a negative Hoffman sign) was 0.5. Based on these findings, they concluded that a positive Hoffman sign slightly increased the likelihood of having CSM, while a negative Hoffman sign did not significantly alter the pre-test probability.
The authors have done a nice job synthesizing and quantifying the limited available data on this topic. Spine providers are clinically aware of the relatively low sensitivity and specificity of the Hoffman sign and most other physical exam findings that contribute to the diagnosis of CSM. We have all seen many CSM patients without a Hoffman sign and plenty of non-myelopathic patients who have a positive Hoffman sign. One of the major limitations of any study on this topic is the lack of a gold-standard to diagnose CSM. While the papers used varying MRI findings as the "gold-standard", this is problematic as many patients can have spinal cord compression and even signal change in the cord without having clinically relevant myelopathy. This may be why there was a 46% prevalence of CSM, which seems very high for a typical spine surgery practice. The authors reported a false negative rate of 41%, which may be artificially elevated given a radiographic diagnosis of CSM (i.e. patients with cord compression without clinically evident myelopathy would not have a positive Hoffman sign yet would be characterized as a false negative). This article helps to hammer home the point that CSM is a clinical diagnosis based on the provider's gestalt after considering findings from the history, physical exam, and imaging. The authors mention doing a prospective study of patients presenting with neck pain who undergo a physical exam and MRI, but such a study would be difficult to carry out. For one, the lack of a gold-standard diagnostic test precludes accurate calculation of test characteristics. Future studies probably need to rely on an expert's clinical impression as the diagnostic gold-standard. Additionally, it would be very difficult to obtain insurance approval for an MRI in a patient presenting only with axial neck pain. A useful exercise in the future may be to create a diagnostic prediction algorithm that includes findings from the history, physical exam, and imaging findings. It is unlikely that such an algorithm would outperform an experienced expert, but it might be of use for generalists or less experienced spine providers.
Please read Dr. Fogarty's article on this topic in the December 1 issue. Does this change how you view the role of the Hoffman sign in the diagnosis of CSM? Let us know by leaving a comment on The Spine Blog.
Adam Pearson, MD, MS
Associate Web Editor