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The cause of steroid
responsive meningitis-arteritis (SRMA) is unknown but is thought to be due
to an autoimmune disease process causing inflammation of the meninges (the
covering layer of the central nervous system) and peripheral nerve roots. It
also affects arteries and tissues in many of the body’s systems.
Autoimmune disease
occurs when something within the dog’s environment acts as a trigger factor,
causing the immune system to become confused. This results in the immune
system no longer recognising its own body parts as ‘itself’ but as foreign
to the body, like bacteria. The immune system automatically mounts an attack
to destroy the ‘invader’ but in reality it set to destroy part of its own
body, resulting in an autoimmune disease. There are various autoimmune
diseases that affect different systems of the body and SRMA is just one of
these diseases. A genetic predisposition is required for a dog to develop an
autoimmune disease, and is often more prevalent in certain families. Some
breeds are more prone to SRMA than others, and an association with
vaccination has been recorded in Weimaraners.
SRMA is a
non-infectious, inflammatory disease usually affecting young animals. It can
be cyclic in nature but the initial onset of the disease is usually sudden,
showing symptoms such as: high temperature, neck stiffness, intense pain -
especially around the neck and ears, general body stiffness, sensitive to
touch and depression. Characteristically, the dog may stand with his neck
stiff and held low, just below horizontal, almost as if frightened to move.
Initially, a severe ear infection may be suspected, although speculative
treatment with anti-inflammatory drugs and antibiotics will show no
improvement in the dog’s condition.
Diagnosis is achieved
by physical and neurological examination, and spinal fluid analysis,
revealing elevated protein and white cells typical of central nervous system
inflammation.
SRMA responds very
well to immunosuppressive treatment of prednisolone (2mg/kg/day) or a
combination therapy of prednisolone and azathioprine (2mg/kg/day or
alternate days) reducing steroid therapy to alternate days and weaning off
all treatment over a period of months. A dog on high dose steroids should be
given a gastroprotectant, such as Zantac, to minimise irritation to the
stomach.
The prognosis for
patients with SRMA is generally very good, although relapses may occur at
any time. Recovery is usually rapid and improvement can be seen with hours
of giving immunosuppressive therapy, hence the name steroid responsive
meningitis.
SRMA can occur with
polyarthritis. The arthritis is symmetrical and non-erosive and confirmed by
synoval fluid biopsy. Polyarthritis/meningitis syndrome is recognised in
several larger breeds.
References:
Clinical Immunology of the Dog & Cat by Michael J Day
Canine Medicine & Therapeutics by Neil Gorman
Clinical Medicine of the Dog and Cat by Schaer
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