MUO in pets - Meningoencephalitis of Unknown Origin

MUO stands for "meningoencephalomyelitis of unknown origin" and is an umbrella term for immune-mediated inflammatory diseases of the brain, spinal cord, and meninges. MUO encompasses several variants, including granulomatous encephalitis (GME), necrotizing meningoencephalitis (NME), and necrotizing leukoencephalitis (NLE). These conditions occur mainly in dogs and lead to severe neurological symptoms. In cats, MUO is rare.

In this article, we discuss the causes, symptoms, diagnosis, treatment, and prognosis of MUO in pets.

What is MUO?

MUO is a presumed immune-mediated brain and/or spinal cord disorder in which the immune system mistakenly attacks the nervous tissue. It causes inflammation in the brain, spinal cord, and meninges.

Which animals are at risk?

MUO occurs most often in dogs, with 75% of cases affecting small to medium-sized breeds such as the Pug, Maltese, and Yorkshire Terrier. In 25% of cases, it is seen in more atypical dog breeds. The condition usually occurs in young to middle-aged dogs. In cats, MUO is rare.

Causes of MUO

The exact cause of MUO is unknown. Because the exact cause is unknown, the term "unknown origin" is used. MUO is most likely an autoimmune disease and is not contagious. Factors that may play a role include genetic predisposition, immune system dysregulation, and environmental factors. To date, there is no evidence that MUO has an infectious cause.

Symptoms in dogs and cats

Symptoms vary depending on the location and severity of the inflammation:

• Behavioral changes
• Blindness
• Paralysis

Diagnosis of MUO

The diagnosis of MUO is made using MRI and a cerebrospinal fluid tap. On MRI, we typically see areas of inflammation, and inflammatory cells are seen in the cerebrospinal fluid. Histopathological examination is the only definitive test. Since a brain biopsy is rarely performed in veterinary medicine, this is mainly done post mortem. To rule out infectious causes, blood samples and cerebrospinal fluid samples are additionally sent to an external laboratory.

Treatment of MUO

Medication

Treatment consists of long-term immunosuppressive therapy. This often involves a combination of corticosteroids and other immunosuppressive agents (including cytarabine, cyclosporine, azathioprine, etc.).

Supportive therapy

Additional supportive therapy may be needed depending on the symptoms. Alongside medication, intensive care is important. Physiotherapy can help with the recovery of coordination and muscle strength.

Recovery and prognosis

The prognosis for MUO is guarded, with a survival rate of 60-65%. Some dogs respond well to therapy and can remain stable long-term. Others develop progressive symptoms despite treatment.

Want to know more?

Read more about our services in neurology and internal medicine. Our specialized veterinarians at Nesto have experience diagnosing and treating MUO and guide you and your pet through the treatment process.

Frequently asked questions (FAQ)

What is MUO?

An immune-mediated inflammation of the brain and meninges in dogs, the cause of which is unknown.

Which animals are at risk?

Mainly small to medium-sized dogs of young to middle age. In cats, the condition is rare.

How is the diagnosis made?

With an MRI and a cerebrospinal fluid tap, after ruling out infections and tumors.

How is MUO treated?

With long-term immunosuppressive therapy, usually a combination of corticosteroids and additional agents.

What is the prognosis?

Caution. There is an average survival rate of 60-65%.