'Hummingbird Sign' in Fragile X-Associated Tremor/Ataxia Syndrome
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Authors: Paolo Immovilli, Eugenia Rota, Nicola Morelli, Ilaria Iafelice, Fabia Cavallotti, Emanuele Michieletti and Donata Guidetti
Article first published online: 30 MAR 2015 | DOI: 10.1002/mdc3.12162
A 64-year-old man progressively developed ataxic gait, 3-Hz high-amplitude, intentional/postural tremor, and dysarthric speech.
FMR1 gene analysis revealed a premutation (89 CGG repeats) and a brain MRI showed mesencephalon atrophy with normal pons morphometry (the so-called “hummingbird” or “penguin” sign) along with middle cerebral peduncle hyperintensity, the radiological hallmark of fragile X-associated tremor/ataxia syndrome (FXTAS).
The disease achieved mild severity in 2 years: Neither psychiatric symptoms nor dementia or impairment in daily living activities were reported.
In Figure 1, the axial/coronal MRI (A–D) shows the hyperintensities in the MCP. The volumetric/magnetization-prepared rapid gradient echo data provided a Parkinsonism Index [(P/M) × (MCP/SCP)] (2) value of 14.4 (normal value: <13.55), indicating mesencephalic atrophy. The sagittal images (E and F) show mesencephalic volume loss configuring the so-called hummingbird sign (SCP, superior cerebellar peduncles; MCP, middle cerebellar peduncles; P, pons area; M, midbrain area).
Figure 1. Axial (A and C) and coronal (B and D) MRI show the hyperintensities in the middle cerebral peduncles, sagittal images (E and F) reveal the “Hummingbird sign”.
Herein, an MRI sign highly specific for PSP was detected in FXTAS, consistently with further neuroimaging evidence of midbrain degeneration[1, 2]; hence, we suggest to take into account FXTAS in the diagnostic workup whenever the hummingbird sign is found outside the typical PSP clinical picture.