Understanding Masticatory Muscle Myositis Dog Head Sunken in Above Eye Causes and Recovery

Masticatory muscle myositis is a condition that affects dogs, causing their head to appear sunken above the eyes. This is due to inflammation of the muscles involved in mastication, or chewing.

The condition is often seen in young to middle-aged dogs, with a higher incidence in certain breeds such as German Shepherds and Rottweilers. Inflammation of the muscles causes pain and stiffness, leading to a characteristic sunken appearance above the eyes.

Symptoms can include difficulty eating, drooling, and a reluctance to move the jaw. The condition is typically diagnosed through a combination of physical examination, medical history, and diagnostic tests such as electromyography and muscle biopsy.

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Masticatory myositis is a condition that affects the muscles used for chewing.

The muscles of mastication are crucial for the intricate process of chewing, and they include the temporalis, digastricus, masseter, and pterygoid muscles.

The muscles of mastication contain myosin fibers, which are fundamental structures found in all muscles.

One type of myosin fiber unique to the muscles of mastication is called 2M fibers.

Patients with masticatory myositis develop marked inflammation in their chewing muscles due to an immune system attack on the 2M fibers.

The body creates antibodies that target specific components of the 2M fibers, including myosin heavy chain, myosin light chain 2-masticatory (LC2-M), and masticatory myosin binding protein-C (mMyBP-C).

Serotonin may also promote fibrosis, or scarring, in the muscles of mastication.

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Masticatory muscle myositis can be a challenging condition to diagnose, but it's essential to catch it early to provide the best care for your furry friend.

Symptoms can be vague and may be mistaken for other conditions, such as inflammation of the tonsils or enlarged lymph nodes under the jaw and neck. Initially, the acute phase may include lethargy, fever, unwillingness to eat, and drooling.

As the condition progresses, the chronic form of masticatory myositis may include muscle shrinkage, difficulty opening the mouth to eat, anorexia/weight loss, and sunken eyes due to loss of muscle mass.

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Your veterinarian may suspect MMM based on bloodwork, which can show anemia, an increase in certain white blood cells, and an increase in muscle enzymes. A thorough oral examination under anesthesia may also be recommended to rule out other conditions.

A specific blood test called the 2M antibody ELISA assay can help diagnose masticatory muscle myositis, but a muscle biopsy is often needed to determine the progression of the disease and subsequent prognosis.

Symptoms can be a bit tricky to spot in dogs with Masticatory Myositis, as they can be similar to other conditions. Lethargy is one of the first signs, often accompanied by a fever.

Fever is a common symptom, but it's not always easy to notice. Your dog might not show any other obvious signs, making it hard to diagnose. Drooling is another symptom that can be a sign of Masticatory Myositis.

As the condition progresses, symptoms can become more pronounced. Muscle shrinkage is a common sign, making the bones of the head more prominent. This is a result of the inflammation and muscle wasting.

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Difficulty eating is another symptom that can be a challenge for dog owners. Your dog might have trouble opening its mouth to eat, making mealtime a struggle. Anorexia and weight loss can also occur as a result of the condition.

The eyes can also be affected, appearing sunken due to the loss of muscle mass. This can be a concerning symptom, but it's essential to note that it's a result of the condition, not a separate issue.

To diagnose masticatory myositis, veterinarians rely on a combination of physical examination, blood tests, and imaging studies.

A thorough oral examination under anesthesia is often necessary to rule out other conditions that may be causing the symptoms. During this examination, the veterinarian will look for signs of muscle weakness or wasting in the jaw muscles.

A panel of bloodwork may show anemia, an increase in certain white blood cells, and an increase in muscle enzymes such as creatine kinase (CK) and aspartate aminotransferase (AST). These changes can indicate muscle damage or inflammation.

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A specific blood test called a 2M antibody ELISA assay can help diagnose masticatory myositis by detecting circulating autoantibodies to the 2M fibers. However, this test may not always be conclusive, especially if the dog has been treated with steroids.

A muscle biopsy is often necessary to determine the progression of the disease and subsequent prognosis. This involves removing a sample of muscle tissue to examine for signs of inflammation and muscle damage.

Here are some conditions that may need to be ruled out before a diagnosis of masticatory myositis can be made:

Treatment for masticatory muscle myositis typically involves immunosuppressive therapy that can last weeks to months, or even lifelong.

The goal of treatment is to aggressively halt the immune system's attack on the muscle and return the dog to normal as quickly as possible.

Corticosteroids, such as prednisone, are often prescribed at immunosuppressive doses for at least 30 days before tapering the dose.

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Other immunosuppressive drugs, like azathioprine, cyclosporine, and mycophenolate, may be used in combination with corticosteroids to combat inflammation.

Medications should be given as prescribed, and owners should work closely with their veterinarian to prevent relapse.

Relapse can occur if medications are given at inappropriate doses or for too short a period.

To manage pain, dogs may need other pain medications until steroids reduce inflammation and circulating antibodies.

Successful feeding may require softening dry food or using calorie-dense liquid formulations.

Masticatory myositis can be a recurrent condition, and each recurrence can be more difficult to treat.

The prognosis declines with subsequent episodes of the disease due to fibrous changes to the muscle.

Dogs with extensive muscle fibrosis have poorer prognoses, making early identification and treatment essential.

A common problem is the incorrect treatment of MMM, which can lead to relapse and worsening of the disease.

Immunosuppressive dosages of corticosteroids should be used until the normal range of jaw motion returns and serum CK returns to normal.

The dosage should then be gradually decreased until the lowest alternate day dosage is reached that will keep the dog free of clinical signs.

This dosage should be continued for at least 6 months to prevent relapse.

A treatment plan may involve partnering with a board-certified veterinary internal medicine specialist to develop a logical and cost-effective plan.

Early identification and treatment are crucial to prevent permanent damage to the muscles and improve prognosis.

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The 2M antibody assay is a specific test that can help diagnose masticatory muscle myositis (MMM) in dogs. It's an Enzyme-Linked Immunosorbant assay (ELISA) that detects antibodies against type 2M fibers and proteins.

This test provides the specificity needed to separate MMM from other neuromuscular diseases like polymyositis, which affects both masticatory and limb muscles.

The 2M antibody assay is particularly useful because it doesn't detect antibodies in dogs with denervating disorders or other neuromuscular diseases.

However, false negatives may occur if the dog has been on immunosuppressive dosages of corticosteroids for longer than 7-10 days or if the MMM is end-stage with destruction of type 2M fibers and marked fibrosis.

In these cases, the test may not provide an accurate diagnosis, and other tests like a muscle biopsy may be necessary to confirm the presence of MMM.

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The key to managing masticatory myositis is early identification and intervention.

Early intervention can maximize the likelihood of a meaningful response.

Therapies are aimed at thwarting the immune system attack, relieving pain, and ensuring adequate nutritional support.

Relieving pain is crucial to prevent further muscle damage and improve the dog's quality of life.

By addressing the condition promptly, you can help your dog feel more comfortable and reduce the risk of long-term complications.