Tongue-Tied: Post-Stroke Symptoms And The Tongue-Out Test

The tongue can be a useful indicator of whether someone is having a stroke. The tongue is controlled by both sides of the brain through the hypoglossal nerve, which determines its movement. If someone is having a stroke, their tongue may appear crooked or twisted to one side, while the other side of the tongue will appear flat and smooth. This is known as tongue deviation and has been observed in both ancient and modern times. Tongue deviation was found to be present in 29% of stroke victims in one study. However, it is not always a reliable indicator as it is often difficult for the layperson to assess and interpret.

Tongue deviation can be a warning sign of stroke

Tongue Deviation: A Warning Sign of Stroke

The tongue is a sensitive area of the human body, with extensive neural controls. The hypoglossal nerve, which controls the tongue, is a pure motor nerve that can be affected when the motor cortex in the brain is damaged. This can cause the tongue to deviate towards the side of the lesion, a condition known as tongue deviation. Tongue deviation is a symptom observed in stroke patients, and it has been recognized as such for thousands of years in traditional Chinese medicine.

The presence of tongue deviation can be a crucial warning sign of an impending stroke. However, there is a lot of room for interpretation when it comes to the tongue deviation test. The challenge lies in quantifying the features of tongue deviation and scientifically verifying the relationship between the deviation angle and a stroke.

A study by Ching-Chuan Wei et al. proposed a quantification method for the tongue deviation angle to characterize stroke patients. They captured tongue images of stroke patients, transient ischemic attack (TIA) patients, and normal subjects to analyze the effectiveness of their method. The results showed significant differences in the tongue deviation angle between the patient groups (stroke and TIA patients) and the normal group. A tongue deviation angle greater than 3.2 degrees may indicate a risk of stroke.

Tongue deviation can be a simple, reliable, and non-invasive means for the prognosis of ischemic stroke patients. By recognizing this warning sign, individuals may be able to obtain medical help quickly, potentially preventing a stroke or reducing its severity.

Tongue deviation is often difficult for the lay public to assess and interpret

Tongue deviation is a symptom of stroke or transient ischemic attack (TIA). When the motor cortex in the brain is damaged, the hypoglossal nerve, which innervates the muscles of the tongue, is affected. This results in the tongue deviating towards the side of the lesion when protruded.

While tongue deviation is a recognised symptom of stroke, there is a lot of room for interpretation in the tongue deviation test. The challenge lies in quantifying the features of tongue deviation and establishing a clear relationship between the deviation angle and a stroke. The tongue deviation test lacks an effective quantification method, which is crucial for its reliability.

To address this, a study proposed a quantification method for the tongue deviation angle to characterise stroke patients. This method involved capturing tongue images of stroke patients, TIA patients, and normal subjects, and analysing the deviation angles. The results showed significant differences in the tongue deviation angles between the patient groups and the normal group, indicating that the tongue deviation angle can effectively distinguish between these groups.

The study also highlighted the variation in visual examination findings between different physicians, which further emphasises the need for a standardised quantification method. Visual illusion, where the eye perceives images that differ from objective reality, can impact the accuracy of tongue deviation assessments. Therefore, a quantification method is essential for clinical application to reduce errors and improve the reliability of stroke diagnosis and monitoring.

The hypoglossal nerve controls the movement of the tongue

The hypoglossal nerve, also known as the twelfth cranial nerve, is responsible for controlling the movement of the tongue. It is a nerve with a sole motor function, supplying all the extrinsic and intrinsic muscles of the tongue except for the palatoglossus, which is controlled by the vagus nerve.

The nerve arises from the hypoglossal nucleus in the medulla, the bottom part of the brainstem, and passes through the hypoglossal canal in the skull before travelling down through the neck and eventually back up over the tongue muscles it supplies. The hypoglossal nerve then divides into branches that supply and control the tongue muscles.

The nerve is involved in controlling tongue movements required for speech and swallowing, including sticking out the tongue and moving it from side to side. Damage to the nerve or the neural pathways that control it can affect the ability of the tongue to move and its appearance. The most common sources of damage are injury from trauma or surgery, and motor neuron disease.

When the hypoglossal nerve is damaged, the tongue may appear to have a "bag of worms" look (fasciculations) or wasting (atrophy) when at rest. If a person with nerve damage sticks their tongue out, it will usually deviate to one side due to the genioglossus muscle receiving nerve signals on one side but not the other. Weakness of the tongue muscles caused by nerve damage can result in slurred speech, particularly for sounds that are dependent on the tongue for generation.

The tongue can deviate after a stroke due to damage to the corticohypoglossal pathway

The corticohypoglossal pathway is a crucial component in understanding the impact of a stroke on tongue deviation. This pathway involves the corticohypoglossal projections, which are responsible for the control of tongue movement. Damage to this pathway can result in tongue deviation, with the tongue deviating towards the side of the lesion.

The corticohypoglossal pathway consists of the corticobulbar fibres that originate in the peri-Sylvian area of the motor homunculus. These fibres descend through the internal capsule, cerebral peduncle, and corona radiata before crossing the midline at the pontomedullary junction. However, it is important to note that individual variations in the decussation location of these fibres have been reported.

When a stroke occurs, it can damage the lower motor neuron for voluntary motor control of the tongue, resulting in muscle weakness and tongue deviation towards the side of the lesion. This is often accompanied by dysarthria and dysphagia, which can significantly impact an individual's quality of life.

The direction of tongue deviation provides essential clues for localising the brain lesion. In most cases, a brain stem lesion will result in an "uncrossed hemiparesis", with the tongue deviating to the side of limb weakness, contralateral to the brain lesion. However, exceptions to this pattern exist due to the bilateral inputs to the hypoglossal nucleus and variations in the corticohypoglossal fibres decussation.

The corticohypoglossal pathway is an important area of focus in understanding and managing tongue deviation following a stroke. By studying this pathway, clinicians can gain insights into the complex interplay between brain structures and their impact on motor functions, particularly those related to tongue movement and deviation.

Tongue biting can be used to distinguish epileptic seizures from syncope

A study by Brigo et al. (2012) found that there was a significantly higher prevalence of tongue biting in patients with epileptic seizures (odds ratio of 12.26). The sensitivity of tongue biting for the diagnosis of generalized tonic-clonic seizures was 24%, and the specificity was 99%. Lateral tongue biting was 100% specific to grand mal seizures. Pooled accuracy measures of tongue biting for the diagnosis of epileptic seizures were: sensitivity 33%, specificity 96%, positive likelihood ratio 8.167, and negative likelihood ratio 0.695.

Another study by Brigo et al. (2012) found that tongue biting may occur in both epileptic seizures and psychogenic non-epileptic events (PNEEs). However, a pooled analysis of data showed that lateral tongue biting, but not non-specific tongue biting, has diagnostic significance in distinguishing seizures from PNEEs. The pooled accuracy measures of tongue biting (no further specifications) were sensitivity 38%, specificity 75%, positive likelihood ratio 1.479, and negative likelihood ratio 0.837. Pooled measures of lateral tongue biting were sensitivity 22%, specificity 100%, positive likelihood ratio 21.386, and negative likelihood ratio 0.785.

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