Overview

Idiopathic trigeminal neuropathy (ITN), sometimes called dropped jaw syndrome, is a condition that affects the trigeminal nerves. The trigeminal nerve, or cranial nerve V, controls the muscles used to close the jaw and provides sensation to the face. Dogs with ITN develop a sudden inability to close their mouth. Although the inability to close the mouth can look alarming, ITN is generally not considered a painful condition. The biggest challenge is maintaining adequate nutrition and hydration until the nerve recovers. The condition is usually temporary, and most dogs recover within a few weeks with supportive care.  

Although most cases resolve on their own, dogs with sudden jaw weakness should always be evaluated promptly, as other medical conditions can cause similar signs and may require different treatment.

Cause

The exact cause of ITN is unknown, and dogs of any breed can be affected.

The current evidence suggests it may result from inflammation of the trigeminal nerve, possibly immune-mediated, though this has not been definitively proven. Most cases occur without an identifiable cause. 

Less commonly, jaw dysfunction of the trigeminal nerve can be associated with other diseases such as certain types of cancers, infectious diseases, or other neurologic conditions affecting multiple cranial nerves. 

Clinical Signs

The hallmark sign is a sudden, non-painful inability to close the mouth, often described as a “dropped jaw.” Affected dogs commonly have difficulty eating, drinking and excessive drooling.

Less commonly, some dogs may also have reduced sensation to parts of the face, a weak or absent blink reflex, muscle loss around the head, or signs of Horner syndrome (droopy eyelid, raised third eyelid, small pupil, sunken eye).

Diagnosis

There is no single test to definitively diagnose ITN. Diagnosis is based on your dog’s history, a physical exam and a neurologic exam to rule out other conditions that can cause similar signs, such as a jaw fracture or other neurologic disease. 

Bloodwork, including evaluation of thyroid function, may be recommended. Advanced imaging, such as MRI, may also be recommended to rule out tumors or other structural abnormalities. Some cases can show signs of nerve inflammation on MRI, but not all.

Treatment

There is no specific medication for ITN, and treatment focuses on supportive care while the nerve heals. Helping your dog eat and drink is often necessary to ensure adequate nutrition and hydration while reducing the risk of accidentally inhaling food or water, which can lead to aspiration pneumonia. This often involves feeding a watered-down, gruel-like consistency that most dogs are able to lap up. Severe cases may require a temporary feeding tube placed by a veterinarian. 

Your veterinarian may consider placement of a temporary tape muzzle, which can be used to hold the mouth partially closed while the nerves are recovering. Other supportive care may include topical eye lubrication if blinking is reduced to prevent corneal injury, and gentle range of motion exercises of the jaw, as recommended by your veterinarian.

Outcome

The prognosis for ITN is very good, with most dogs recovering within 2-3 weeks. Most dogs regain normal jaw function and can return to eating and drinking normally once the nerve recovers. 

Some dogs may have a longer recovery period of up to 10 weeks, particularly if they develop significant muscle loss of the jaw muscles (atrophy). Less commonly, dogs may only partially recover or experience repeat episodes.