Pain and psychological disturbances are more common causes of aggression than cerebral disease. Aggression from pain is either due to touching the painful area or the animal avoiding such contact. Treating the source of pain generally restores the animal’s personality to normal.
It is reasonably common for dogs to be presented for neurological assessment after biting all the family members, sometimes more than once, over a period of time. In many instances, the owner admits to wanting a guilt-free reason for euthanizing the pet and thinks that an MRI of the brain is the answer. Neurological and physical examinations and history typically fail to find any abnormality.
If the owner is willing to accept and manage the risks of aggression and will agree to treat either an underlying brain disease or a psychological disturbance then MRI would be of value to the dog as it would aid treatment choices.
There was a 2-month history of hindlimb ataxia. Once-yearly generalized seizures, which had first been noticed at 2 years of age. The last seizure occurred 2 months prior to referral at which time phenobarbitone was commenced. Since then, the dog had urinated in her bed, defecated indoors, not greeted visitors and had snapped at the owner twice.
The dog was alert and ambulatory with hindlimb ataxia. Hindlimb hopping and proprioception were reduced in both hindlimbs. Forelimb function was normal. Spinal reflexes were normal. Spinal pain could not be elicited by palpation.
The lesion was localized to the T3–L3 spinal cord segments owing to the hindlimb weakness as demonstrated by the decreased ability to hop, the reduced proprioceptive ability of the hindlimbs and the presence of intact spinal reflexes in both hindlimbs. Intact spinal reflexes signify that the lumbosacral intumescence is intact and so the cause of weakness must be further rostral. In an ideal world where diagnosis is easy, all animals with UMN paralysis or paraparesis would have ‘textbook’ hyperreflexia.
The seizures began years ago and the dog had not developed any behavioural abnormality until recently. Seizures may result from small frontal lobe lesions which with time will expand and cause inter-ictal neurological deficits. As a general rule of thumb, such deficits would have been expected to appear within 1 year. The age of onset of seizures and normal inter-ictal period is highly suggestive of idiopathic epilepsy. Post-ictal behaviour change and ataxia can occur but would not be expected to last 2 months. Low serum phenobarbitone levels can cause hyperactivity but not aggression. Polyuria and polydipsia are side-effects of phenobarbitone and this may result in urination in the house if the animal is not allowed outside to eliminate more frequently.