The central nervous system (CNS) is the control centre for the body. It is made up of the brain, spinal cord and the covering of these, the meninges. Meningitis refers to inflammation of the meninges.
What is steroid responsive meningitis-arteritis?
In dogs, steroid responsive meningitis-arteritis (SRMA) is an ‘immune mediated’ or ‘auto-immune’ disease. Dogs in the UK are less prone to infection of the central nervous system (CNS) than humans in part because of vaccinations.
Animals can suffer from many different immune-mediated conditions. It is unclear what the underlying mechanism is, but it involves the immune system attacking a protein (foreign substance or antigen) it encounters in the environment, or minor infections caused by bacteria, viruses, or parasites that match a protein in the body, causing an abnormal inflammatory reaction.
SRMA is an immune-mediated disease that affects the arteries in the covering of the nervous system (the meninges), but other areas in the body can be affected such as the joints.
What causes SRMA?
It is usually impossible to determine why an animal develops an immune-mediated disease like SRMA. Exactly why the immune system suddenly becomes ‘confused’ and attacks the CNS remains a mystery. Dogs of any breed can be affected by SRMA, but dogs of certain breeds such as Boxers, Beagles, Bernese mountain dogs, and Weimaraners are most commonly affected. The condition is probably caused by a complex interaction between genetics and the animal’s environment.
The juvenile immune system appears to produce inflammation and antibodies (protective proteins made by the immune system in response to foreign substances or antigens) in response to a normal body protein – in SRMA, a protein expressed by blood vessel walls in the meninges.
As this condition does not cause an infection, it is not contagious.
How would I know if my dog has SRMA?
As a result of SRMA, pain, stiffness of gait, reluctance to move the neck, hunched back, and often fever are the main symptoms – this pain is usually severe in the neck but can also be present to a lesser extent in the lower back. The pain is greatest when trying to touch the chin to the chest. There are no other neurological abnormalities expected with this condition. In most cases, dogs won’t eat and won’t exercise.
Inflammation can affect other parts of the body, including the joints. Joint swelling can cause dogs to walk stiffly and stiltedly. There is a chance that animals with SRMA may experience inflammation of other inner body surfaces, such as the heart’s covering (potentially leading to abnormal heart rhythms), lungs, and abdominal contents (causing the formation of some fluid).
How will my vet know if my dog has SRMA?
It is unfortunately not possible to diagnose inflammatory CNS disease merely by observing the patient’s symptoms. The diagnosis is usually established by excluding other causes of spinal pain (such as bone or soft tissue infections, immune-mediated joint diseases, infections) through blood tests and x-rays. Under general anaesthesia, spinal fluid is collected in a sterile manner from the neck or lower spine (or both). Identifying inflammation and inflammatory cells will facilitate a presumptive diagnosis. A panel of tests is normally run to exclude the possibility of infection, although it is very unlikely this will be present.
Can SRMA be treated?
The answer is yes, and, in the long run, most dogs will be able to lead normal lives. In order to counteract the ‘over-excitation’ of the immune system, the mainstay of treatment for SRMA is suppressing the immune system with drugs, especially high doses of corticosteroids like prednisolone. It is very common for high doses of steroids to result in significant and rapid improvements or resolutions of clinical symptoms after being administered by injection or given orally. A gradual reduction of the dose is then implemented over several months until the immune system is no longer stimulated.
The use of steroids is often associated with side effects. Steroids produce side effects such as increased thirst and hunger (resulting in urination and weight gain), lethargy, panting, and increased risk of infections (respiratory, urinary, etc.).
It is occasionally necessary to add additional medications to suppress the immune system or to reduce the steroid dose without fear of relapse. Although many of these second-line drugs are technically chemotherapy drugs, they are used at relatively low and safe levels with few side effects. When patients are hospitalized, cytosine araboniside (Cytarabine) is commonly injected. Oral medication such as cyclosporine and azathioprine can also be taken.
The side effects of medication will be discussed with you by your veterinary neurologist or primary care veterinarian.
Will my dog recover from SRMA?
Most patients with SRMA improve after 2–3 days of treatment and enter clinical remission within 2 weeks of starting treatment.
In most cases, steroid treatment is required for 5–7 months, after which treatment can be stopped and a normal life can be led.
There is a possibility of relapse after treatment has been stopped or during treatment. There is a 20% relapse rate among patients with SRMA. Clinical signs will be similar or identical to those of the original syndrome if relapse occurs. When a treatment regimen is ‘stepped back’, relapses are normally treated successfully.
As part of the treatment, you may have to visit your veterinarian from time to time. Every few months, your veterinarian may recommend blood tests to assess the function of organs affected by the treatment. Depending on the individual’s response to treatment, this may need to be repeated periodically.
Don’t hesitate to contact your vet if you have any concerns about your dog’s treatment.