The Modified Glasgow Coma Scale (MGCS) has been adapted from the human Glasgow Coma Scale (GCS) which was created in 1974 as an objective way to assess the level of consciousness in humans following a traumatic brain injury and coma. The assessments are performed at initial presentation and repeated several times a day during hospitalisation to monitor the patient for progression of neurological signs (Trub, 2016) (Table 1). The GCS was modified for use in veterinary patients in 1983 by the Chief of Neurosurgery and Neurology as the Mississippi State University College of Veterinary Medicine. The scale was proposed as an objective way to evaluate the neurological status of dogs after traumatic brain injury, assess overall prognosis and evaluate neurological function alongside the neurological examination (Trub, 2016). Although the scale was developed specifically for head trauma patients, it can be used to monitor any patient with changes to level of consciousness, including patients that are quieter than usual to those which are comatose. In these patients, the scale is useful to indicate severity and any improvement or decline of neurological function and can act as a prognostic indicator to advise and inform clinical decisions and communicate prognostic information to owners (Trub, 2016). The three areas the MGCS evaluates are level of consciousness, motor activity and brain stem reflexes and each is given a score between 1 and 6. The evaluation and reasons behind the evaluation are discussed below.
Modified Glasgow Coma Scale (MGCS)
| Score | |
|---|---|
| Motor activity | |
| Normal gait, normal spinal relexes | 6 |
| Hemiparesis, tetraparesis or a decerebrate rigidity | 5 |
| Recumbent, intermittent extensor rigidity | 4 |
| Recumbent, constant extensor rigidity | 3 |
| Recumbent, constant extensor rigidity with opisthotonus | 2 |
| Recumbent, hypotonia of muscles, depressed or absent spinal reflexes | 1 |
| Brainstem reflexes | |
| Normal pupillary light reflex and oculocephalic reflexes | 6 |
| Slow pupillary light reflex and normal to reduced oculocephalic reflexes | 5 |
| Bilateral unresponsive miosis with reduced oculocephalic reflexes | 4 |
| Pinpoint pupils with reduced to absent oculocephalic reflexes | 3 |
| Unilateral, unresponsive mydriasis with reduced to absent oculocephalic reflexes | 2 |
| Bilateral unresponsive mydriasis with reduced to absent oculocephalic reflexes | 1 |
| Level of consciousness | |
| Occasional periods of alertness and responsive to environment | 6 |
| Depression or delirium, capable of responding, but response may be inappropriate | 5 |
| Semi comatose, responsive to visual stimuli | 4 |
| Semi comatose, responsive to audio stimuli | 3 |
| Semi comatose, responsive only to repeated noxious stimuli | 2 |
| Comatose, unresponsive to repeated noxious stimuli | 1 |
| MCGS | Score |
| 3–8 | Grave |
| 9–14 | Guarded |
| 15–18 | Good |
The MGCS is used alongside the monitoring of vital parameters including heart rate, respiratory rate and blood pressure (Aldridge and O'Dwyer, 2013). As in any emergency situation, airway, breathing and circulation should be assessed first. If an animal is hypoxic as a result of a respiratory injury or severely hypovolaemic then any mentation changes will be exacerbated (Aldridge and O'Dwyer, 2013). Blood pressure, specifically mean arterial pressure, is valuable as it relates closely to cerebral blood flow, so can give information about blood flow and thus oxygenation to the brain (Aldridge and O'Dwyer, 2013). Hypotension with bradycardia is an indicator of the Cushing reflex, which occurs when intracranial pressure is critically high so knowing the patient's baseline and picking up on any trends will give prior warning of increasing intracranial pressure (Aldridge and O'Dwyer, 2013).
Motor activity
Assessment of motor activity is the first part of the scoring system. If the patient is able to ambulate normally this is easy to assess by asking them to walk out of the kennel. However, if the patient is recumbent then other methods need to be used to assess motor function, which are part of the MGCS and described below. As well as assessing the patient's ability to ambulate and the gait pattern, which can be described as different forms of paresis or even plegia, spinal reflexes can also be tested. Spinal reflexes give information relating to the spinal cord, predominantly localising a lesion to the upper or lower motor neurons. There are many spinal reflexes described, however the easiest to perform and interpret are the withdrawal reflex and the patella reflex (Chiang et al, 2024).
Withdrawal reflex
This spinal reflex is tested by applying a noxious stimulus to the limb being tested by pinching the toe with fingers (Figure 1). This unconscious stimulus causes a reflex contraction of the flexor muscles and withdrawal of the tested limb (Chiang et al, 2024).
Withdrawal reflex
Patella reflex
The patellar reflex is performed by tapping the patellar tendon with a patella hammer or a finger (Figure 2). To be able to perform this test accurately the patient's pelvic limb needs to be relaxed. Ideally the patient should be positioned in lateral recumbency with the limb being tested upper-most; however, it can be performed in a standing position if the patient is supported. A positive response to the test is stifle extension when the patella tendon is tapped. This reflex assesses the femoral nerve and its associated spinal cord segments (L4-L6) (Chiang et al, 2024). It is important to also consider the patient's signalment, as this reflex can be lost in older animals as a normal finding (Lowrie, 2014).
Patella reflex
The biceps brachii and triceps reflexes can be used to assess the thoracic limbs. The triceps reflex assesses C7 to T1 spinal nerves and peripherally the radial nerve. The bicep reflex assess C6 to C8 spinal nerves and, peripherally, the musculocutaneous nerve. However, the reliability of the thoracic limb reflexes is inconsistent in most patients and so must be interpreted in the context of the full examination, not as an isolated examination finding (Freeman and Ives, 2020).
Hemiparesis, paraparesis and tetraparesis
Hemiparesis is a term used to describe weakness in the muscles and more broadly suggests a reduced ability to generate normal voluntary movements and therefore a normal gait pattern (Freeman and Ives, 2020). This can be as a result of the muscles being too weak to support the body or may be due to a disruption in the signals from the brain stem via the spinal cord to the peripheral nerves which in-nervate the limbs (Freeman and Ives, 2020). Hemi refers to one side of the body being affected and tetraparesis refers to all four limbs being affected (Figure 3). Paraparesis is the term used to describe when both hind limbs are affected and is commonly seen in dogs with a spinal lesion caudal to the T2 spinal cord segment (behind the shoulders), such as an extruded intervertebral disc (Platt and Olby, 2017).
Tetraparetic dog being helped to stand with a harness.
Decerebrate extensor rigidity
Decerebrate extensor rigidity is extension rigidity of all limbs, head and neck (referred to as opisthotonos). The rigidity occurs as a result of a loss of communication between the cerebrum and the brain stem (Platt and Garosi, 2012). This is a posture that occurs in patients with a severely affected level of consciousness, which makes it questionable why a score of 5 in the MGCS is possible, and shows how the use of a system such as the MGCS should only be used as a guide and all assessments should be taken alongside a full clinical picture and not assessed in isolation. This posture carries a very poor prognosis and despite a score of 5 being given in the MGCS, it should be treated as a neurological emergency (Freeman and Ives, 2020).
Decerebellate rigidity
Decerebellate rigidity is another posture displayed by patients with possible brain damage, which will cause hyperextension of the forelimbs similar to decerebrate rigidity, however, the pelvic limbs will be flexed. There will be no altered mentation with this posture, the patient will remain alert and responsive which is the most obvious way to differentiate it from the decerebrate rigidity (Platt and Garosi, 2012).
The motor score for the patient can easily be affected by other comorbidities such as limb or spinal injuries in multi-trauma cases, which can result in a falsely decreased score which should always be considered when preforming the assessment (Freeman and Ives, 2020).
Brain stem reflexes
Pupillary light reflex
The pupils should always be assessed at rest and from a distance first, check for any asymmetry in size referred to as anisocoria (de Lahunta et al, 2020). The pupillary light reflex is tested by shining a light into one pupil (direct pupillary light reflex) and observing if the pupil changes size. The light is then shone into the opposite pupil (consensual pupillary light reflex) to see if that affects the pupil size. This is then repeated on the opposite pupil to check for any differences (de Lahunta et al, 2020).
When performing a pupillary light reflex it is imperative to take into account the stress response and how that will cause pupil dilation and reduce their normal response to light, which would be especially important when assessing cats. Therefore, assessments may be easier in a calm, dark environment. Pupillary light reflex assessment assesses cranial nerve II (optic nerve), cranial nerve III (oculomotor nerve) and their connection to the brain stem. It is important to remember it is not an assessment of vision (Webb and Cullen, 2013).
Mydriasis and miosis
In a healthy animal the pupils will be equal in size and respond in the same way to stimuli. The size of the pupil will be determined by the environmental light and emotional status of the animal. The most common finding is that one pupil is normal and one is either inappropriately dilated or constricted (Heller and Bentley, 2016). It is therefore important to work out which is the abnormal one. One easy way to do this is to examine the patient in both bright and dark environments and observe how the pupils respond (Heller and Bentley, 2016).
Possible causes of a large (mydriatic) pupil may be as simple as low light levels causing dilation to maximise the amount of light able to reach the retina or stimulation of the sympathetic nervous system in response to stress, pain or exercise. Iris atrophy (which is common in older dogs) causes shrinkage and weakness of the iris sphincter muscle, resulting in enlargement of the pupil and can also cause sluggish pupillary light reflexes (Heller and Bentley, 2016). Some other ophthalmic conditions can also cause pupil enlargement (Heller and Bentley, 2016).
Dilated pupils also occur when intracranial pressure is increased because of the location of the pupillomotor nuclei in the brain. The pressure exerted on the brain causes disinhibition of the nerve fibres (Heller and Bentley, 2016). Prognosis is guarded when miosis (small pupil) is detected, and becomes grave after mydriasis with absent pupillary light reflex is identified. Treatment to decrease intracranial pressure should be started as soon as possible (Heller and Bentley, 2016). Raised intracranial pressure can be treated in a number of ways including simply raising the patients head by 30° or medically by administering an osmotic diuretic such as mannitol, which draws fluid from tissues and cells into circulation. If raised intracranial pressure is suspected, jugular blood samples should be avoided and patients should be kept as stress free as possible (Bell, 2020).
Oculocephalic reflex/vestibulo-ocular reflex
Oculocephalic reflex, also referred to as the ‘vestibulo-ocular reflex’, is tested by gently moving the patient's head from side to side while watching for movement of the pupils. The pupils should move in a coordinated way to realign the gaze with that of the head direction (Freeman and Ives, 2020). An abnormal finding would be the pupils staying still (as if painted on, like a doll's eyes, hence why this reflex is sometimes called the doll's eye reflex). This reflex is coordinated by the vestibular system, which includes parts of the cerebellum, thus patients with disorders of the vestibular system can have an absent, incomplete or slow corrective movement of the eye when the head is moved (Freeman and Ives, 2020). Lesions affecting the brainstem will also result in a reduced or poor vestibulo-ocular reflex, but will be accompanied by a reduced level of mentation, tetraparesis and other cranial nerve deficits, such as a poor gag reflex, miosis or anisocoria (Figure 4) (Freeman and Ives, 2020). A completely absent or incomplete vestibulo-ocular reflex may be seen in brain stem compression secondary to raised intracranial pressure and herniation of the brain, therefore it is an important assessment in the MGCS, especially following head trauma (Freeman and Ives, 2020).
Anisocoria
Level of consciousness
In a normal, healthy patient, they will appear bright, alert and will explore their environment. They will respond to visual, auditory and tactile stimulation and interact with those around them (Olby, 2010). The mental status of the patient is a combination of level of consciousness and behaviour. It is helpful therefore to have an idea of what normal is for the patient from a detailed history and to be able to describe and document these findings precisely (Olby, 2010). Subtle changes in the patient's responsiveness could easily be missed if multiple members of the veterinary team are dealing with the case. Therefore, in an ideal situation, there would be one member of staff, such as the nurse, predominantly monitoring the patient to enable subtle changes to be noted and for the veterinary team to be made aware of changes rapidly. Allowing time for thorough handovers is also vital for continuity of care so the team are aware of the patient's status and can act quickly if deterioration is detected.
Level of consciousness is controlled by the ascending reticular activating system. It is a bundle of neurons which extends through the brainstem and projects into the thalamus and cortex. The ability to interact appropriately with the surrounding environment depends on the ability to process sensory information and combine this information with previously learned information. The forebrain, and in particular the cerebrum and limbic system, are therefore vital for normal behaviour (Olby, 2010). When intracranial pressure increases and puts pressure on this area, the neurons are unable to respond normally and changes to behaviour and mentation are apparent.
If mental status deteriorates, the patient may become less responsive to normal stimulation. This is described as depression or obtundation. Knowing what is normal to that particular patient relies on a thorough handover between staff and a precise history from the owner (Olby, 2010). If the patient deteriorates further this is termed stupor, and is a decreased level of consciousness where the patient may be in sternal or lateral recumbency, and may be difficult to rouse, but is able to respond to strong stimulus such as noxious stimulation (Olby, 2010). If the patient deteriorates even further they will become comatose. This term describes a patient as unresponsive to any stimulation.
Conclusions
The MGCS is a useful indicator for prognosis but it is important to remember that although it gives an objective measure it is a subjective assessment, and results may vary based on the examiner's experience and the patient's temperament. Additionally, repeat evaluations are necessary to monitor changes in the neurological status over time. It is vital nurses are familiar with the components of the scale and understand how to perform the assessment as part of nursing care plans and be confident in interpreting the results in a way that contributes to providing optimal care for patients experiencing neurological challenges.