Introduction:
The tongue is an important organ of the human body. It is important for functions like speech, swallowing, deglutition, and chewing. Proper neural innervation is essential for the smooth functioning of the tongue muscles. Any problem in the neural innervation may cause paralysis of the tongue.
What Is Hypoglossal Nerve Palsy?
The hypoglossal nerve is the twelfth cranial nerve that is known to innervate the muscles that control mainly the movements of the tongue (except for the palatoglossus muscle). The palatoglossus muscle is innervated by the vagus nerve (cranial nerve X). The hypoglossal nerve is associated with multiple movements needed for actions performed by the tongue. For example, actions like chewing food or mastication, swallowing, and speech production are linked directly to the functioning of the hypoglossal nerve.
The condition of isolated hypoglossal nerve palsy is an uncommon occurrence. On the other hand, bilateral hypoglossal nerve palsy is common. But it is also one of the significant diagnostic challenges poised not only for general physicians but also for dentists.
The majority of cases reported are linked with an underlying malignancy (that affects the functions of the hypoglossal nerve). Other causes of hypoglossal nerve palsy are; trauma, cerebral stroke, neuropathies, post-surgical trauma, or neurologic infections. The pathogenesis of this nerve palsy is not clearly explained yet by researchers as the exact or clear mechanism for these features or damage to the nerve remains elusive
These conditions are often associated with possibly other cranial nerve palsies other than hypoglossal or twelfth cranial nerve. Hypoglossal nerve palsy is a rare condition. So far only a hundred major cases are documented in the medical literature (associated with twelfth cranial nerve palsy) linked either to an underlying cancer or malignant tumor or with other traumatic or infectious causes.
What Are the Clinical Features of Hypoglossal Nerve Palsy?
Most of the patients are affected by isolated bilateral hypoglossal nerve palsy. The affected individuals may present with clinical features such as dysarthria (difficulty in pronouncing words), saliva accumulation in the oral cavity, drooling of saliva, inability to swallow properly, dysphagia or difficulty in swallowing food, inability to force or propel food towards the pharynx, dyspnea (difficulty in breathing) in the supine position, difficulty in raising the tongue or move the tongue.
It is essential to note that mild clinical features like features of mild dysphagia (difficulty in swallowing) or dysarthria (improper or unclear speech articulation) in patients may also be suggestive of hypoglossal nerve palsy. In such cases, many of the patients might not have any other subjective complaints. Because of this, the condition may have been left unattended or untreated. Dentists should watch out for typical signs of this disease like diminished mobility of the tongue or limited movements when the patient tries to deviate the tongue towards the affected side. In the case of unilateral hypoglossal nerve palsy, the limitation would be more while trying to perform or deviate the tongue through movement to the affected side.
On the other hand, patients suffering from bilateral hypoglossal nerve palsy may show the presence of dysarthria and dysphagia symptoms, because of which they report to the physicians or the dental surgeons with this chief complaint.
What Are the Causes of Tongue Paralysis?
Paralysis of the tongue can be either partial or complete. It can be caused either by advanced cases of isolated bilateral or by advanced cases of unilateral hypoglossal nerve palsy. Though researchers are elusive about the nature or mechanisms that lead to paralysis, the reasons are usually linked to trauma or certain types of traction injuries occurring to the hypoglossal nerves at the base of the skull region. Individuals who are suffering either from genetic malformations or genetic disorders, at the base of the skull may also be prone to developing hypoglossal nerve palsy. Most cases that are diagnosed and treated in time usually are known to have a good prognosis as well as good long-term recovery.
What Are the Diagnostic Methods of Hypoglossal Nerve Palsy?
The diagnostic tests that are done for this purpose are:
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Magnetic Resonance Imaging (MRI): It is considered to be the best imaging technique in order to visualize the causes of nerve palsy. It can be used for conditions like diagnosing epidural hematomas. However, in severe cases (where infection or cause has been left untreated), such patients may be suffering from cardiorespiratory instability that can prevent them from undergoing this diagnostic testing.
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MASA: According to Neurologists, the ideal diagnostic test for isolated bilateral or unilateral hypoglossal nerve palsy can be made by the Speech Intelligibility Rating (SIR) test. The patients are rated through this test with their values assessed based on the following criteria; a clinical evaluation, eating assessment tool, mann assessment of swallowing ability (MASA) test, and tongue pressure test.
Usually after admission, the patients are inserted with a nasogastric feeding tube and attempts are made to swallow or for chewing rehabilitation. Speech therapy can be initiated post-treatment for these patients In addition, physical therapy is an important way forward to tongue muscle strengthening and training.
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Electromyography: It is another important technique that can be utilized for revealing signs of neurological damage. For diagnosing neurological damage a patient's tongue is observed along with the fibrillation potentials for analyzing the minimal active contraction of the motor units.
What Are the Differential Diagnosis of Hypoglossal Nerve Palsy?
It is important for the surgeon to differentiate hypoglossal nerve palsy from other nuclear or intranuclear lesions that can also produce tongue-related paralysis, atrophy, and fasciculations. Some supranuclear lesions of the brain may also be related to the moderate to severe inability of tongue functions. Hence it is crucial that oral surgeons who might come across oral manifestations like dysphagia, inability to perform tongue movements, and dysarthria should take prompt action and differentiate it from other conditions.
How to Manage Hypoglossal Nerve Palsy?
The main treatment strategies for hypoglossal nerve palsy include the use of surgical interventions, immobilization, or rehabilitation therapies. The surgical strategy is hypoglossal nerve transfer or gracilis tissue transfer (surgical procedure for facial reconstruction purposes) for treating paralysis symptoms. These can not only support the long-term recovery of tongue functions but it is usually associated with a good prognosis of innervating the hypoglossal nerve again. Also, physiotherapy and never stimulus can be helpful in regaining nerve function.
Conclusion
The hypoglossal nerve is important for the proper functioning of orofacial structures. Conditions like cancer, trauma, infection, and stroke may lead to hypoglossal nerve palsy. It is a difficult condition to diagnose. Proper examination and diagnostic tests are helpful in identifying this pathological condition. Timely intervention is required for the treatment of hypoglossal nerve palsy.
