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

Area of Science:

• Neurology
• Radiology
• Medical Imaging

Background:

• The hummingbird sign (HBS) is a key indicator differentiating progressive supranuclear palsy (PSP) from idiopathic Parkinson's disease (IPD).
• Current identification of the HBS lacks standardized criteria, hindering consistent clinical communication and research.

Purpose of the Study:

• To establish consensus criteria for HBS identification by developing a novel radiologic rating scale (HBS-RS).
• To evaluate the inter-rater reliability (IRR) and diagnostic validity of the HBS-RS.

Main Methods:

• T1 midsagittal MRI scans from 133 patients (93 IPD, 40 PSP) were reviewed by two blinded raters.
• The HBS-RS, comprising four weighted items (third ventricle floor contour, beak shape, head shape, midbrain atrophy), was used for assessment.
• Inter-rater reliability and diagnostic validity were assessed using established statistical methods.

Main Results:

• The HBS-RS demonstrated moderate-to-good inter-rater reliability (Cohen's kappa, 0.479-0.766), with the third ventricle floor contour showing the highest agreement.
• Sensitivities for individual items were high (85.0-92.5%) at lower thresholds.
• Composite scores of the HBS-RS achieved over 80% specificity and fair diagnostic accuracy for PSP (AUC, 0.76 and 0.73).

Conclusions:

• The HBS-RS provides a simple, measurable tool for objective HBS assessment in clinical and research settings.
• The scale offers adjustable diagnostic validity for progressive supranuclear palsy.
• Standardized HBS identification through the HBS-RS can improve communication and diagnostic consistency.