Meningoencephalitis of unknown origin (MUO):
Meningoencephalitis is the inflammation of the brain and meninges. which is a thin membranous layer coating the brain. MUO is an immune-mediated condition in which the white blood cells of the body attacks the central nervous system – the brain, spinal cord, and occasionally the optic nerves. Magnetic resonance imaging (MRI) of the affected area and cerebrospinal fluid (CSF) tap are diagnostics that are usually used to diagnose this condition. Because there may be infectious causes of meningoencephalitides (bacteria, viruses, fungal) infectious agent testing may be submitted as part of the diagnostic workup.
There are three main types of MUO: granulomatous meningoencephalitis (GME), necrotizing meningoencephalitis (NME), and necrotizing leukoencephalitis (NLE). Despite the type of MUO, the treatment is the same across the board with immunosuppression to stop the body’s white blood cells from attacking the neural tissues. Prednisone is the mainstay therapy and it is usually used in conjunction with other immunosuppressive medications to provide better control of the disease, depending on the needs of the individual patient.
Myasthenia gravis (MG):
Myasthenia gravis is a disease of the neuromuscular junction that results in generalized
weakness in dogs and cats. Acquired myasthenia gravis is an autoimmune disease that can occur spontaneously and acutely. Antibodies produced by the body’s white blood cells attack receptors for acetylcholine (a neurotransmitter responsible for muscle contraction) on the muscle. This results in a decreased number of functional acetylcholine receptors and prevents the muscles from functioning properly, leading to weakness. The clinical signs include increased lethargy, exercise intolerance, inability to walk, facial weakness, inability to blink, or even collapse. This condition often leads to esophageal dilation (megaesophagus) in dogs, which can result in regurgitation of food from the stomach. Aspiration pneumonia is a severe secondary effect of regurgitation.
To diagnose this condition, chest x-rays should be performed to check for signs that myasthenia gravis, such as megaesophagus and to ensure that there is no aspiration pneumonia. A Tensilon test and electrodiagnostics (repetitive nerve stimulation) can also be performed. The most definitive test is an antibody titer against acetylcholine receptor and this is a blood test that can be submitted to the laboratory.
Steroid responsive meningitis arteritis (SRMA):
SRMA is an autoimmune disease that results meningitis. Meningitis is a condition in which ther is inflammation of the meninges, which is a thin membrane that covers the brain and spinal cord. Clinical signs include fever, neck, back, and head pain. This condition usually occurs in young dogs and breeds that are predisposed to this condition include German Shorthaired Pointer, Boxer, Bernese Mountain Dog, and Beagle. Diagnostics include imaging of the spine (x-ray and MRI) and a cerebrospinal fluid (CSF) tap. Measurement if the immunoglobulin A (IgA) antibody in the CSF is highly indicative of SRMA. Infectious agent testing may also be performed to rule out infection. Treatment is with long-term immunosuppressive corticosteroids.
Immune-mediated polyarthritis (IMPA):
As the name of the condition suggests, this is an immune-mediated disorder resulting in joint effusion and pain. It is important to understand that other conditions such as infections, conditions resulting in vasculitis, severe degenerative joint disease, and cancer can also result in joint effusion. Other immune-mediated processes can also result in joint effusion.
IMPA occurs when the body produces antibodies against membranes in the joint and usually occurs in young dogs. Certain breeds predisposed to such conditions include Siberian Huskies and their crossbreeds and Bernese Mountain Dogs. Diagnoses include x-rays of the affected joints and performing joint taps to submit samples of the synovial fluid for cytology and possibly culture to rule out infection. Treatment for IMPA is with long-term immunosuppressive corticosteroids. Occasionally, adjunctive immunosuppressive medications may be required.