Cranial Neuritis - Types, Symptoms, and Treatment

Introduction:

Nerves are wire-like structures that carry impulses between the brain and other body parts. The word cranial refers to anything related to the skull. Cranial nerves are the nerves that are present at the base of the brain located within the skull. The functions of the cranial nerves can be sensory, motor, or both. Sensory functions of the cranial nerves include the ability of a person to see, hear, taste, and smell. The motor functions of cranial nerves include controlling muscle movements, especially those in the head and neck region.

What Is Cranial Neuritis?

Cranial nerves transmit signals between the brain and different regions of the neck, head, and torso (the region between the base of the neck and hip). Cranial neuritis is the inflammation (swelling) of one or more of the cranial nerves that are a total of twelve in number. Cranial neuritis can lead to demyelination (a condition in which the protective outer layer which surrounds the nerves in the brain is damaged) or damage to the cranial nerves. Neuritis that affects a single nerve is known as mononeuritis. Neuritis, which affects several single nerves simultaneously, is referred to as mononeuritis multiplex. When nerves that are well separated from each other are affected, it is known as polyneuritis.

What Are the Types of Cranial Nerves and Their Functions?

The cranial nerves are 12 in number, and each one has a specific function. They have been numbered by using the Roman numerals I to XII. The names of the cranial nerves, along with their functions, are as follows:

1. Olfactory Nerve: Transmits information about the sense of smell to the brain.

2. Optic Nerve: Transmits information about the vision to the brain.

3. Oculomotor Nerve: Controls the movements of the eye muscles (moving of the eyeballs, upper eyelids, and blinking of eyes).

4. Trochlear Nerve: Helps to move the eyes upwards, downwards, outwards, and inwards.

5. Trigeminal Nerve: Carries sensations of the face and helps in jaw movements like chewing.

6. Abducens Nerve: Helps in eye movements, especially in looking outwards.

7. Facial Nerve: Helps in expressions of the face and taste sensation.

8. Vestibulocochlear Nerve: Helps in a person’s sense of balance and hearing.

9. Glossopharyngeal Nerve: Sensation of the throat, abilities like taste and swallowing.

10. Vagus Nerve: Regulation of heart rate, movement of muscles involved in breathing and digestion.

11. Accessory Nerve: Helps in muscle movements of the neck and shoulder, like a person’s ability to extend or rotate his neck and shoulder.

12. Hypoglossal Nerve: Helps in the movement of the tongue.

What Are the Causes of Cranial Neuritis?

Researchers have found that the following factors are responsible for causing cranial neuritis.

• Infections:

  • Certain viral, bacterial, and fungal infections are thought to play a role in causing cranial neuritis.

  • Examples of viral infections that may be responsible for cranial neuritis are Varicella-zoster virus (the virus that causes chickenpox), Dengue virus (the virus responsible for dengue fever), and Epstein-Barr virus (a virus that causes infectious mononucleosis which is reflected as fever, extreme tiredness and sore throat that is highly transmissible infection).

  • Examples of bacterial infections are Mycobacterium tuberculosis (bacteria responsible for causing tuberculosis which is a very serious and highly transmittable disease affecting the lungs), Borrelia burgdorferi (bacteria that causes Lyme disease, which shows symptoms like extreme tiredness, fever, headache, and skin rashes), and Treponema pallidum (bacteria that causes syphilis which is an infection that is transmittable through sexual contact).

  • Examples of fungal infections include Cryptococcus neoformans (fungi that cause cryptococcus neoformans infection, which initially affects the lungs followed by the brain and spinal cord), Mucormycetes (fungi that causes mucormycosis infection, which is characterized by lung infections and face swelling), and Aspergillus (fungi that are responsible for causing aspergillosis which shows symptoms like severe cough, fever and breathing difficulties).

• Autoimmune Diseases:

  • The immune system present in a person’s body protects him from infections and diseases by destroying the bacteria, viruses, or any other foreign body that is responsible for the infection. Autoimmune disease is a condition in which a person’s immune system attacks the healthy cells of his own body.

  • Examples of autoimmune diseases are polyarteritis nodosa (a disease that causes swelling of blood vessels leading to the injury of internal organs) and systemic lupus erythematosus (a disease that is characterized by fever, joint pain, and damage of organs like skin, kidney, and brain.

• Neoplastic Causes:

  • Neoplasm indicates an abnormal growth found in any part of the body, which mostly shows the features of cancer.

  • Certain tumors (abnormal mass of tissue) present near or within the brain and spinal cord may cause swelling and damage to the cranial nerves.

  • Chemotherapy is the usage of powerful chemicals to destroy the cancer cells in the body.

  • In some cases, chemotherapy can lead to damage and swelling of the cranial nerves, which is known as chemotherapy-induced neuritis.

• Others:

  • Rare disorders like idiopathic recurrent polyneuritis cranialis, which can affect multiple nerves, may cause cranial neuritis.

  • Patients with diabetes and migraine are also seen to develop complications that affect the cranial nerves.

  • Severe head injuries like skull fractures, blows on the head, and falls may cause an impact on the brain leading to swelling of the cranial nerves.

What Are the Common Symptoms of Cranial Neuritis?

• Severe headache, which lasts for a long period.

• Tingling or burning sensation in the facial and neck areas.

• Reduced ability to sweat.

• Pricking type of pain in the facial or neck areas.

• Persons with neuritis of the oculomotor nerve may experience double vision, drooping of upper eyelids, and uncontrolled movement of the eyeball, which makes the eyes deviate outwards and downwards.

• Patients with neuritis of the trochlear nerve may have the look of one eye positioned above the other or a difference in the alignment of both eyes.

• Patients with neuritis of the trigeminal nerve may experience severe electric shock-like pain, which may last for a few minutes. The patient has difficulty in simple tasks like chewing food, brushing his teeth, and speaking.

• Patients with neuritis of the abducens nerve may have one eye that is deviated towards the nose, and the patient cannot move the affected eye outwards.

• Patients with neuritis of the facial nerve have symptoms like paralysis of the face, pain around the jaws or ear, drooling (the involuntary act of excess saliva coming out of the mouth), loss of taste, reduced tear production, and deviation of the face towards one side.

• Patients with neuritis of the vestibulocochlear nerve may feel as if the environment around them is spinning, uncontrolled circular movements of the eye, hear a ringing noise in the ears, and decreased hearing abilities.

• Neuritis of the glossopharyngeal nerve may lead to swallowing difficulties, loss of taste sensation, and the inability of the patient to contract the throat to prevent choking (an object blocking the throat causing difficulty in breathing).

• Neuritis of the vagus nerve leads to difficulty in swallowing, shortness of breath, decreased heart rate, and indigestion.

• Neuritis of the accessory nerve leads to drooping and pain in the shoulders.

• Neuritis of the hypoglossal nerve leads to weakness and paralysis of the tongue.

How to Diagnose Cranial Neuritis?

• Neurological Examination: The doctor conducts a thorough examination to test the patient’s ability to balance, experience sensations, and respond to reflexes. The patient is made to move his eyes in all directions, following a moving target like the tip of a pen or finger.

• Electromyography (EMG): This test is performed to detect the activity and health of the muscles both at rest and during work. It helps to find out the weakening or improper functioning of the muscles and problems in carrying signals from nerves to the muscles.

• Computed Tomography (CT) Scan and Magnetic Resonance Imaging (MRI): These imaging tests are done to obtain a clear picture of the brain. Computed tomography shows an indirect view of the cranial nerve and its path of exit through the hole present at the base of the skull. It helps to find out any abnormalities in the structure and path of the nerve. Magnetic resonance imaging provides a clearer picture of cranial nerve abnormalities. A contrast agent called gadolinium is incorporated into the magnetic resonance imaging technique. This helps to attain a clearer picture of the cranial nerve and helps to find out any abnormalities like a tumor, nerve damage, disturbances in the blood and brain barrier, and any signs of fracture in the skull.

• Nerve Conduction Velocity Test: This test is done by attaching two electrode patches to the patient’s body. One electrode conducts a mild electrical impulse to the nerve, and the other electrode records it. This test helps in understanding the activity of the nerve and detects nerve damage.

• Cerebral Angiography: This test uses a catheter (thin needle-like tube), an X-ray machine, and an injection of contrast agent. This is mainly done to find out any abnormalities in the blood vessels of the brain.

• Lumbar Puncture and Blood Tests: Lumbar puncture is done by pricking and inserting a needle in an area in the lower back of the patient to get a sample of cerebrospinal fluid (the colorless fluid that flows in and around the brain and spinal cord). This helps to find out any infectious disease of the brain which may be the underlying cause of cranial neuritis. The doctor may ask the patient to perform a blood test to find out signs of diabetes (high blood sugar level) which may be the underlying cause of cranial neuritis.

• Hearing Tests: In patients with neuritis of the vestibulocochlear nerve, hearing and balance tests are to determine if a portion of the nerve has been damaged due to the swelling. A head impulse test to find out the patient’s ability to stay focused during fast head movements is also done. The uncontrollable eye movements of the patient indicate vestibular neuritis.

How Is Cranial Neuritis Treated?

The treatment options for cranial neuritis may vary depending on the cranial nerve involved and the symptoms experienced by the patients. They are as follows:

• Medications to reduce pain and swelling are given to the patient. If the neuritis is due to any underlying bacterial, viral, or fungal infection, medications to treat the underlying cause are given to the patient.

• In some cases of neuritis, surgery may be required to correct the nerve abnormalities or to remove the tumor that might be the underlying cause of the neuritis.

• In cases of trigeminal neuralgia (abnormality of the trigeminal nerve), microvascular decompression is done. It is a technique in which the neurosurgeon opens the skulls and views the affected nerve. A small sponge is placed between the blood vessel (that is compressing the nerve) and the affected nerve. This helps the patient to get relief from the pain.

• In patients with an inability to close their eyes, the doctor may ask the patient to use moisturizing eye drops during day time and an eye ointment at night to keep the eyes moist. The patient is also asked to wear glasses during the day and to use an eye patch at night to prevent getting poked.

• Paralyzed muscles may shrink permanently with time. Hence to prevent this, exercises and massage of facial muscles instructed by a physical therapist are found to be highly beneficial.

• In severe cases of facial deformities, plastic surgery may be advised to make a face look symmetrical and to restore the functions of facial muscles. Examples of this surgery are eyebrow lifts, eyelid lifts, and facial implants (prostheses used to enhance facial contours).

Conclusion:

Some cases of cranial neuritis are not dangerous as they get better with time without any treatment. However, cranial neuritis is a condition that should be dealt with extreme care as it involves the nerves which directly originate from the brain. Hence, any suspicious symptoms must be noted, and immediate medical care should be taken at the earliest. Leading a healthy lifestyle by exercising regularly, and having a balanced diet, thereby managing blood sugar and blood pressure levels, can prevent neuritis that is caused due to conditions like diabetes.