Diseases of the Nervous System

1) Fits

EPILEPSY= Paroxysmal, disorganised electrical discharges within the brain.

The occurrence of an epileptic electrical discharge leads to the outward sign of a FIT

(= CONVULSION, ICTUS or SEIZURE), when involuntary muscle activity occurs.

Most fits involve tonic + clonic muscle activity. Tonic = sustained muscle contraction or spasm, Clonic = cycling contraction / relaxation (often described as "paddling" by the owners). Fits often begin with collapse then a period of tonic muscle activity followed by clonic muscle activity.

If the fit persists for longer than 5 or 10 minutes, or the animal goes straight from one fit into the next, then STATUS EPILEPTICUS is said to have occurred. This is much more dangerous than a single simple seizure, as the muscle activity causes a large rise in body temperature, and brain damage or death may occur.

PARTIAL SEIZURES may occur as local brain irritation leading to focal motor activity such as a limb twitch, or tremor. These can be very dificult to identify for sure as epilepsy. Asking the owner to video an episode can be helpful.

Causes of Fits:

a) Primary brain disease- Trauma, hydrocephalus, idiopathic epilepsy, infection (e.g. meningitis), space occupying lesion (e.g. abscess, tumour, tapeworm cyst).

b) Secondary metabolic disease- hypoglycaemia, hyper- and hypo-calcaemia, hypothyroidism, hyperlipidaemia, liver shunts, uraemia, poisonings (heavy metals, metaldehyde, chocolate (!)).

Stages of an epileptiform fit:

a) Pre ictal phase- may not be obvious, but some animals show behavioural peculiarities as the electrical activity begins in the brain. The majority of animals with true epilepsy (i.e. not diagnosed as due to a secondary cause) will begin their fit from sleep or whilst at rest.

b) Ictal phase. electrical activity sweeps across the brain and consciousness is lost. Motor activity begins - owners are often unable to detect that the animal is not conscious, as the eyes may be open and there may be inadvertent response to noise or light stimuli. There is paddling, salivation, vocalisation, loss of bladder and bowel control. Usually brief (minutes).

c) Post ictal phase. Restlessness, wandering and confusion. This can last for some time (hours), and although not dangerous to the animal, it can be very distressing for the owner. Advise that it is only safe to handle the pet when it can recognise the owner, otherwise there is a risk of being bitten

Dealing with the fitting animal:

The first contact is usually with a distressed owner over the phone, often demanding immediate attendance at home by the entire practice.

It is very important to remain calm, and to communicate this to the client. Fits are often very brief, and are subsiding by the time the client has actually telephoned the practice. It is quite important to differentiate between a fit and a collapse or faint, as the latter conditions may well need emergency attention at the surgery if the dog or cat remains collapsed. (See later for how to differentiate).

When you have established that this is a true fit, then advise the owner that it is important to provide a non-stimulating environment for the animal. (Darkened room, no noise or people). Stroking it to calm it is both dangerous and may prolong the fit. Make it clear to the owner that most fits are brief, and it is only if the actual motor activity persists that attendance at the home is a necessity (status epilepticus). Arrange for the owner to leave the animal in a quiet situation, and ring them back in 5 minutes to check on progress. If the dog is distressed in the post-dromal phase, it may be necessary to attend, but this is not a desperate emergency. It is generally better to wait until the patient is more or less normal again, then arrange for it to attend surgery for a check over.

Treatment:

Acutely, fits are treated with valium, midazolam or phenobarbitone, or a combination depending on response, preferably by intravenous injection.

Pentobarbitone injection can be used as a last resort, but this is VERY respiration depressing, so must be used with care.

In status epilepticus, if the body temperature is > 106F then cerebral oedema will be starting and this must be addressed also ( Mannitol, steroids, cooling the patient).

Long term, most dogs are maintained on phenobarbitone by mouth. Other drugs can disturb control fairly easily, so levels in the blood must be monitored. Cats can be given phenobarbitone as well.

2) Unconsciousness / Collapse

Unconsciousness is loss of awareness and loss of non reflex responses. It is usually accompanied by collapse, although in many ways, animals in a fit are unconscious. The important differential is between collapse (syncope) and fitting.

Causes of unconsciousness:

Brain trauma, anoxia (circulatory or respiratory failure), hypoglycaemia, hypokalaemia, hypocalcaemia, poisons and drugs (anaesthetics), heat stroke, hypothermia, narcolepsy.

Collapsed animals will usually need urgent attention at the surgery, unlike fitting animals.

Nursing action: Monitor vital signs including temperature, check airway and begin cardiopulmonary resuscitaion if indicated. Provide warmth, oxygen.

3) Paralysis and paresis

Paresis= weakness of voluntary muscles, Paralysis = lack of voluntary muscle movement.

Quadri / tetraparesis = paresis in all 4 limbs

Quadriplegia = paralysis in all 4 limbs

Paraparesis / paraplegia = Hind limbs only

Hemiparesis / hemiplegia = down one side (2 ipsilateral limbs).

Paresis or paralysis stems from damage to the nerves or neuromuscular junction. Loss of voluntary movement ability stems from motor nerve lesions, or damage to the muscle or neuromuscular junction..

Loss of reflexes or of control over movement can be due to motor or sensory nerve problems.

It is rare to get a "pure" neurological problem in which damage can be absolutely localised as often several nerves are involved, however most neurological testing is aimed at giving an idea of the location and severity of damage.

The localisation process is usually trying to attempt to find out if paresis is due to high or low CNS (i.e. brain, upper spine, lower spine) lesions, and to find out if sensory nerves are involved or motor nerves, or muscle pathology, or a combination.

Neurological testing:

Gait- observed for weakness or ataxia (poor control of limb position). Intact sensory input usually allows reasonable control over movement.

Wheelbarrow, hopping tests are designed to concentrate on individual limbs.

Tight circle turns test co-ordinating ability

Proprioception or limb placement tests- very sensitive to neurological involvement as opposed to muscle weakness.

Muscle tone- increases in some spinal lesions when loss of controlling nerves "releases" individual limb muscles.

Reflexes- panniculus, withdrawal, anal, patellar- test sensory input and motor output over local sections of the spine.

Schiff-sherrington reflex- rigid extension of the forelimbs after damage to the spine, is a very grave sign, and may be accompanied by paradoxical respiration- the intercostal muscles are paralysed and the chest is drawn passively in and out by the diaphragm.

Nursing care if a spinal injury is suspected:

If the patient is not at the surgery, it is usually better for the long term prognosis if it is brought straight in, even though the owners may be reluctant to do this. It is unlikely that the problem will be made worse by gentle movement if the patient has any use of the affected limbs. If the patient appears to be paralysed, it should be carried in a thick blanket or on a stiff board, and twisting of the spine should be avoided. The nurse can make a rapid assessment of the severity of neurological damage. Neurological loss occurs in the following order: Proprioception->skin pain->voluntary movement->deep pain. Depp pain is usually tested by squeezing the nail bed with a pair of artery forceps. The animal should notice that this hapens, not just withdraw the foot which can be a passive reflex.

Longer term or post operative care involves bladder and bowel maintenance, turning every 2 hours to prevent bed sores, and care for any skin areas affected by secretions. Physiotherapy helps to maintain muscle tone.

4)Muscle pathology

Problems involving the muscles may be presented as neurological disease or may be part of a larger problem involving the nervous system also. Types of muscle disease are:

a)Myositis- seen as an immune mediated muscle inflammation, but can also occur as part of the signs of Neosporosis, and Toxoplasmosis.

b) Myopathy- Muscular weakness, seen as an inherited disease in Labradors and Devon Rex cats.

c) Myasthenia gravis- Ususally an acquired disease in larger dogs, in which antibodies are manufactured to the cholinesterase receptors at the neuromuscular junction, leading to extreme muscular weakness. Occasionally seen congenitally.

d)Myotonia- failure of the muscle to relax properly. Seen as an inherited disease in the Chow.

e)Hypokalaemic myopathy of cats- cats in renal failure with low potassium levels show severe muscle weakness.

f) Hypocalcaemia - usually after removal of the thyroid glands in cats, causes muscle twitching and trembling (fasciculation).