By Lynn Broom
Longmead Veterinary Practice.
THE brain is a fascinating and complex organ. We know its basic function involving nerves and electrical impulses, but how it processes experiences, responses and memories is poorly understood.
This lack of understanding leads to significant uncertainty in terms of outcome from brain damage. For instance, a mass such as a tumour may affect brain function in several ways. It can apply local pressure to surrounding tissue leading to loss of function, it can cause inflammation and reduce the working ability of other brain tissue and it can increase pressure within the brain affecting all brain activity.
Brain trauma can present as unconsciousness or altered consciousness. In animals this effect may be short-lived and many apparently normal functions can return quite quickly. The predictability of recovery is, however, impossible to define. Even with imaging, where the area of damage may be identified, the long-term effects can only be determined by patience and time.
Epilepsy can be due to multiple causes. Dogs can develop idiopathic – meaning cause unknown – epilepsy typically between the ages of one and six years and this is thought to be due to an electrical abnormality. Certain breeds are more prone than others. Anti-epilepsy medication is often very effective.
Underlying disease such as diabetes and liver disease can cause altered brain function and seizures. Toxin ingestion is also a possible cause. Very young dogs which develop seizures may have congenital causes – Chihuahuas and French Bulldogs for instance are prone to hydrocephalus which causes increased pressure within the skull. Older dogs which have seizures for the first time are more likely to have a mass within their skull.
Brain tumours may initially cause subtle changes such as loss of co-ordination or localised seizures such as muscle twitching. Due to tumour growth more symptoms develop which can be multiple and can include significant changes in temperament making affected animals dangerous to live with.
Tumours which affect the pituitary gland within the brain are more common in certain breeds such as Boxers. These may cause multiple effects such as increased drinking or excessive hormone production affecting other glands outside of the brain. These tumours are often small and slow-growing and their hormonal effects can often be managed with medication. They can, however, start to affect surrounding brain tissue leading to other symptoms.
Old dog vestibular syndrome is a common cause of weakness and inco-ordination in old dogs. This typically affects the balance system and its cause is usually unknown. It causes ‘flickering’ eyes – nystagmus – and a head tilt with many, but not all, cases spontaneously resolving.
CT and MRI scans allow for identification of any lesions present and allow better determination of prognosis. A dog which has had a subtle bleed or a small area of trauma may well recover fully. A tumour is likely to continue to grow and can cause progressive symptoms leading eventually to death. Symptoms may be controlled in the short term with anti-epileptic drugs and anti-inflammatories but are unlikely to prevent ongoing tumour growth.
Brain-related disease can be unpredictable and difficult to manage but investigation techniques exist to allow identification of the root cause and this allows planning for any future treatment that may be available.