The "upgoing thumb sign" can be used as part of a comprehensive neurological evaluation to help distinguish stroke mimic from actual stroke. It won't replace MRI, but it can be part of the neurological exam, just like we use the Babinski sign. One editorial from 1993 suggested calling it the Hachinski-Babinski, after the discoverer. With the patient's eyes closed during the actual exam, here's how to do it.
Why does this matter?
Much of the neurological exam shows relatively poor inter-rater reliability, such as the commonly used Babinski sign for upper motor neuron disease. This painless test, the upgoing thumb sign - much more pleasant than the Babinski - was more commonly seen in true stroke or TIA than in stroke mimics. It is far from perfect, as is most of the neuro exam, including Babinski, yet we can use this exam finding to understand and localize the patient's presenting neurological complaint.
Once upon a time, Dr. Hachinski, "while examining a 27-year-old woman with a migraine-associated cerebral infarct, noticed a right digit minimi sign. What struck him as much more obvious was the extension of the thumb on the same hand in the extended palms-down position." He decided to have the patient's palms face each other so this would result in an upgoing thumb sign, similar to an upgoing toe sign. This was a systematic study of patients in clinic with stroke mimic vs actual stroke or TIA. Two examiners did the upgoing thumb sign as the first part of the exam, so as not to be biased by the rest of the neuro exam and independently recorded their findings. They found the upgoing thumb sign was seen much more often in true stroke or TIA than in stroke mimic (88% vs 40%, p = 0.001, respectively). And the inter-rater agreement was good, far superior than for the Babinski. Those with stroke mimics who also had an upgoing thumb were much more likely to have had a prior stroke. So how do you perform this wondrous sign? I made a quick video to demonstrate. Again, this sign is not the panacea, but it is a quick, reproducible finding you can use to inform your neurological exam.
Upgoing thumb sign: A sensitive indicator of brain involvement? Neurology. 2017 Jul 25;89(4):370-375. doi: 10.1212/WNL.0000000000004157. Epub 2017 Jun 28.
Peer reviewed by Thomas Davis, MD.