Imaging Techniques Can Improve Accuracy in the Diagnosis of Disorders of Consciousness

S. Andrew Josephson, MD


AccessMedicine from McGraw-Hill 

Patients with disorders of consciousness include those in a persistent vegetative state and those in a minimally conscious state. The distinction between the two conditions has been shown to be important for both prognostication as well as prediction of a state of fluctuating awareness that may allow for some forms of communication. However, multiple studies have demonstrated that clinical diagnoses of these conditions are inaccurate, even when improved through the use of standardized scoring systems such as the Coma Recovery Scale-Revised (CRS-R). A variety of imaging and electrophysiologic techniques have recently been reported to improve the accuracy of these diagnoses, and a recent study (Stender et al., 2014) examined two different neuroimaging techniques in a relatively large and well-characterized cohort of patients.

The authors examined FDG-PET as well as functional MRI (fMRI) in patients with disorders of consciousness. It has been hypothesized that PET can distinguish between patients in a persistent vegetative state and those in a minimally conscious state based on specific areas of hypometabolism in the brain. Using fMRI in patients asked to perform mental tasks such as motor imagery, clinicians may be able to determine patients who have some preserved level of consciousness even when there are no outward signs of such.

The authors included patients referred to their tertiary center with disorders of consciousness over a >4-year period. Repeated CRS-R assessments were used as the reference to calculate the diagnostic accuracy of both imaging methods, and patient outcomes were assessed at 12 months using a standardized scale. A total of 126 patients were included; at the time of referral to the center, they carried a clinical diagnosis of persistent vegetative state (n = 41), minimally conscious state (n = 81), or a locked-in syndrome (n = 4), the latter of which represents a state of normal consciousness. Excluding those patients with ambiguous diagnoses from this group, CRS-R agreed with the clinical diagnosis in 78% of the cohort.

Of the 92% of patients who could be assessed (for technical reasons) with FDG-PET, a high sensitivity (93%) was found for the minimally conscious state and the test correlated well (85%) with CRS-R scores. PET imaging correctly predicted outcome at 12 months in 74% of the patients. In those patients in whom fMRI could be obtained (59%), sensitivity for predicting the minimally conscious state was only 45% with lower correlation (56%) with CRS-R scores. fMRI predicted outcome correctly in 56% of the patients. Importantly, 13 of 42 patients (32%) diagnosed as being in the persistent vegetative state with CRS-R were found to have activity consistent with the minimally conscious state on at least one of the imaging tests, and 69% of these patients were found to regain consciousness at follow-up.

This study once again shows that ancillary studies can improve the clinical diagnosis of patients with disorders of consciousness. The CRS-R scores were used as a reference in the trial, but it appears as if this measure is not a viable gold standard even if it is more accurate than the usual clinical diagnosis. Ultimately, the strength of this study compared with many others is the year-long follow up used to provide outcomes that are the real “gold standard” here. Clinicians should be well aware that these diagnoses can sometimes be in error, and development of adjunctive tests such as these neuroimaging tests (PET being superior in this study to fMRI) can help to improve diagnostic accuracy.