Idiopathic Trigeminal Neuropathy
What is Idiopathic Trigeminal Neuropathy?
Trigeminal neuropathy is a disorder that affects the fifth cranial (aka trigeminal) nerve of the head. The condition is also known as Idiopathic bilateral mandibular nerve paralysis.
There are twelve pairs of nerves which originate at the base of the brain. These are responsible for certain neurological functions of the head and face. These nerves are known as cranial nerves. The fifth cranial nerve is the trigeminal nerve, and it is responsible for the muscles involved in chewing and sensation in the face.
What causes Idiopathic Trigeminal Neuropathy?The term idiopathic indicates that the cause of the condition is unknown. Although some cases of trigeminal nerve disease have an specific origin (e.g. infection, tumors and inflammation of the brain), in this specific disease the cause is not identified. It has been speculated that either inflammation or an immune reaction may cause dysfunction and paralysis of the nerve. All common causes of trigeminal nerve dysfunction must be ruled out to be defined as idiopathic.
What signs might I see in a pet with Idiopathic Trigeminal Neuropathy?
The condition results in paralysis of the muscles of the jaw. If both sides of the head are affected, the lower jaw hangs open and the animal is unable to close its mouth. This appearance is referred to as a “dropped jaw”. In most instances, the animal is unable to eat. Over time, the muscles on the top and sides of the head will shrink in size and the bones of the skull becomes more obvious. As the Trigeminal nerve is associated with sensation on the face, many animals will lose feeling in that location. A lack of sensation may be seen when the pet does not reflectively blink when the eyelids are touched.
In rare cases, animals may have other eye abnormalities, such as drooping of the upper eyelid, sinking of the eyeball and protrusion of the third eyelid so that it partially covers the eye (Horner’s syndrome). Vision remains normal.
What test is generally run to diagnose the condition?Diagnosis is based on physical examination findings and exclusion of other disease that affect the trigeminal nerve. A thorough physical examination, routine laboratory tests, and radiographs may be recommended to search for an underlying cause. Advanced imaging of the brain by magnetic resonance imaging (MRI) or computed tomography (CT scan) may also be recommended.
Is there any treatment?
No specific treatment exist for Idiopathic Trigeminal Neuropathy. Supportive care is important. The animal may require assistance with eating and drinking. Insertion of a feeding tube may be considered in some animals to provide adequate nutrition. If the animal does not blink often, lubricating may be required to the eyes.
Rechecks are usually recommended periodically to assess for improvement of clinical signs and to assess body weight and nutritional status of the pet.
The prognosis for recovery is generally good. Most animals regain nerve function in 2-4 weeks, however a full recovery can take several months in some pets. Some pets only partially recover and in some cases trigeminal nerve function does not return.