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CANINE CHIARI-LIKE MALFORMATION AND SYRINGOMYELIA CM/SM

CM/SM – treatment

Medical and surgical treatment options exist for dogs with Chiari-like malformation with syringomyelia and a possible approach to management is illustrated in Fig 9. The main treatment objective is pain relief.
Due to the persistence of syringomyelia and/or spinal cord dorsal horn damage, it is likely that the post-operative patient will require continuing medical management for pain relief. Also, in the majority of canine patients, medical management alone may be chosen for financial reasons or owner preference. There are three main type of drugs used for treatment of Chiari-like malformation with syringomyelia: drugs that reduce CSF production (acetazolamide, cimetidine, omeprazole or furosemide); analgesics (non-steroidal anti-inflammatory drugs and anti-epileptic drugs that have analgesic properties); and corticosteroids. As yet there are no scientific studies to prove the efficacy of these drugs in the management of neuropathic pain in dogs and recommended management is based on anecdotal evidence only
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The process of CSF production by the choroid plexus epithelial cells involves the enzymes carbonic anhydrase C, sodium and potassium ATPases, and aquaporin-1 and results in the net transport of water, sodium chloride, potassium and bicarbonate ions from the blood into the ventricles .
All medicines should be given under veterinary guidance.

Acetazolamide reduces CSF production by inhibiting carbonic anhydrase C and by reducing the amount of aquaporin-1 through an alteration in protein transcription . The use of acetazolamide for management of Chiari-like malformation and syringomyelia has been described ( and is also used in management of benign intracranial hypertension in humans. However long term use of acetazolamide is often limited by adverse effects, including lethargy, abdominal pain and bone marrow suppression.
Omeprazole is a specific inhibitor of H(+)-K(+)-activated ATPase however it is not clear if this is the mechanism by which it reduces CSF production. In experimental models using a ventriculocisternal perfusion technique, omeprazole reduces canine CSF production by 26%. Histamine (H2)-receptor antagonists such as cimetidine and ranitidine are proposed to reduce CSF production by competitive inhibition of H2 receptors located on the choroid plexus epithelial cell, or by a direct effect on the capillaries of the choroid plexus However there is also evidence that histamine may act physiologically by increasing the electrical activity of vasopressin-secreting neurons .Vasopressin reduces blood flow to the choroid plexus, thereby decreasing CSF production. Cimetidine has been shown to be superior to ranitidine to reducing CSF production in an experimental cat model. The usefulness of omeprazole or cimetidine for Chiari-like malformation, with or without syringomyelia, is unclear. They are often prescribed in the hope that this may limit disease progression, a variable that is difficult to assess in a scientific study of clinical cases. Some owners report a significant improvement in clinical signs of pain. Adverse effects from these drugs are infrequently reported. Cimetidine retards P450 oxidative hepatic metabolism so caution is advised if using this preparation concurrently with other drugs metabolised by the liver and with both cimetidine and omeprazole, periodic monitoring of haematology and serum biochemistry is advised. Absorption of gabapentin may be reduced with concurrent cimetidine administration however the effect is thought to be clinically insignificant (90). It has been suggested that chronic hypergastrinemia, caused by omeprazole, may increase the risk of gastric carcinomas, at least in laboratory rodent models but this has not been reported in any other species .

Use of the diuretic furosemide for management of Chiari-like malformation and syringomyelia has also been described and is also used in management of benign intracranial hypertension in humans. Furosemide may not be ideal in toy breed dogs that also have a high likelihood of mitral valve disease and where the most common cause of death is congestive heart failure. Furosemide can result in significant increase in plasma aldosterone concentration and renin activity in healthy dogs. This early activation of the renin-angiotensin-aldosterone system might be deleterious in an animal predisposed to heart disease. Moreover, long-term use of diuretics can lead to a diuretic-resistant state, which necessitates the use of higher doses, further activating the renin-angiotensin-aldosterone system.

Anecdotally, acupuncture and ultrasonic treatments have been reported to be useful adjunctive therapy in some cases. In some cases physiotherapists are able to help alleviate signs and acupuncture. Care should be taken however as the response to these treatments is very individual and some dogs may actually be more painful afterwards. Spinal manipulation is contraindicated.

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