SRMA, also known as corticosteroid responsive (aseptic) meningitis is an auto-immune disease that targets the leptomeninges and associated vessels. The exact cause is unknown. Studies have suggested a Th2-mediated response with elevated Immunoglobulin A (IgA) levels in the CSF and serum. Elevated IL-8 levels have been noted in the CSF which is associated with invasion of neutrophils into the leptomeninges.
SRMA is mostly seen in medium to large breed dogs with the Boxer, Bernese Mountain Dog, Beagle, Golden Retrievers, German Shorthaired Pointers and Nova Scotia Duck Tolling Retriever possibly being predisposed. In the Beagle, SRMA was been previously labeled as ‘Beagle Pain Syndrome’. Although these breeds seem to be overrepresented with SRMA, it can affect almost any breed of dog. SMRA typically occurs in dogs less than 2 years of age.
Classically, dogs with SRMA present with fever and severe spinal pain. A majority of patients will have neck pain. Dogs will often experience severe allodynia (pain from a non-painful stimulus) and/or severe anticipation of pain. When walking, dogs will typically have a short, choppy gait. Frequently, no specific neurologic deficits will be noted (i.e. proprioceptive / reflex deficits). Extreme lethargy and decreased appetite may also be noted.
The diagnosis of SRMA is made by a combination of imaging studies and a cerebral spinal fluid (CSF) analysis. MRI of the most painful region is often recommended to rule out other causes of spinal pain such as a herniated disc, vertebral malformations, and other causes of myelitis (i.e. infectious). MRI is a non-invasive test, but does require general anesthesia to keep the dog still and comfortable during the procedure. If no structural cause for the spinal pain is found the next step is to perform a CSF analysis. The total nucleated cell count (TNCC), protein level and cytology of the spinal fluid will be evaluated. Classically you will see a marked neutrophilic pleocytosis and elevated protein levels.
It is important to note that a neutrophilic pleocytosis not 100% specific for SMRA and common infectious diseases should be ruled out with serum or CSF titers. The infectious disease testing submitted should be determined based on geographical location and specific exposure risks. Frequently tested organisms include Rickettsial diseases, Toxoplasma, Neospora, Cryptococcus, and Distemper virus. Approximately 46% of dogs with SRMA will have a concurrent immune-mediated polyarthritis. The clinical signs (i.e. short and choppy gait) can look very similar therefore the clinician needs to pay special attention to palpation of the joints in dogs with suspected SRMA. Frequently if polyarthritis is suspected, arthrocentesis can be performed after the MRI while the dog is still under anesthesia.
To help aid in the diagnosis of SRMA a C-Reactive Protein (CRP) can be measured. CRP is an acute-phase protein that is produced by the liver in response to inflammation in the body. A dog with SRMA will frequently have a high CRP level. This test is also useful to monitor how a patient is responding to treatment and to identify if they are relapsing.
Corticosteroids are the cornerstone of treatment of SRMA. Typically prednisone is started with a high initial dose (2-4 mg/kg/day) and then tapered slowly over several months. Common side effects of corticosteroids may include increased eating and drinking, behavior changes, gastrointestinal upset, and weight gain. The vast majority of dogs with SRMA will become clinically normal very rapidly, often in as little as 1 or 2 days. Occasionally, dogs with more advanced disease will require additional immuno-modulating medications. Cyclosporine, azathioprine, and mycophenolate are examples of other medications that have been used in conjunction with corticosteroids to help control the disease.
Treatment typically lasts for at least 6 months depending on the patient’s response. Because clinical remission is often rapid, tapering the prednisone too quickly is a common mistake that can trigger a relapse. Many dogs can be weaned off corticosteroids completely if done slowly (~6 months). Ideally a normal CRP should be obtained before attempting to taper medications. Ultimately a repeat CSF analysis may be needed to confirm a relapse. Should a relapse occur the initial corticosteroid dose should be restarted and then taper more slowly than the first attempt. Some dogs may require a low dose of corticosteroids life-long.
SRMA typically has an excellent prognosis. Usually after 24-48 hours of starting corticosteroids the dog is improving if not yet normal. The lack of a rapid positive response to the steroids should indicate to the clinician that SRMA may not be the cause of the clinical signs or the patient has a more severe variation of SMRA.