A Visual Rating Scale for the Hummingbird Sign with Adjustable Diagnostic Validity

Although the hummingbird sign (HBS) is a distinctive feature of progressive supranuclear palsy (PSP) VS. idiopathic Parkinson's disease (IPD) and other parkinsonian disorders, there are no consensus criteria for its identification.

To develop consensus criteria for the HBS to enable accurate communication between researchers and physicians, we developed a new radiologic rating scale for the HBS (the HBS-RS), and the inter-rater reliability (IRR) and diagnostic validity of the HBS-RS were evaluated.

Two raters blinded to the clinical diagnoses reviewed T1 midsagittal magnetic resonance images of 133 patients with IPD (n = 93) or PSP (n = 40). The existence of the HBS was assessed in two steps that were separated by two weeks; the first was based on their own experience and the second was according to the HBS-RS. The HBS-RS comprises 4 items (contour of the third ventricle floor, shape of the beak, shape of the hummingbird head, and midbrain atrophy), with weighted scores from 0 to 2.

The IRR of individual items in the HBS-RS and of the composite scores showed moderate-to-good agreement (Cohen's kappa [κ], 0.479-0.766) and were observed to be highest for the contour of the third ventricle floor. The sensitivities and specificities varied depending on the cut-off for each item or for the composite scores. The sensitivities for each item were high (85.0-92.5) at a low cut-off (0 VS. 1 or 2). The specificities reached more than 80% when the composite scores of the HBS-RS were used. Receiver operating characteristic curves for the total HBS-RS scores showed fair diagnostic accuracy for PSP (AUC, 0.76 and 0.73).

The HBS-RS is a simple and measurable visual assessment tool to identify the HBS, with adjustable diagnostic validity for PSP. The results suggest that the HBS-RS may be used for objective measurements of the HBS in research and in the clinic.