Nervous system

AMA5 Chapter 13 (p 305), applies to the assessment of permanent impairment of the nervous system, subject to the modifications set out below. Before undertaking an impairment assessment, users of the Guidelines must be familiar with:

• the Introduction in the Guidelines
• chapters 1 and 2 of AMA5
• the appropriate chapter(s) of the Guidelines for the body system they are assessing
• the appropriate chapter(s) of AMA5 for the body system they are assessing.

The Guidelines take precedence over AMA5.

Introduction

5.1 AMA5 Chapter 13 ‘The central and peripheral nervous system’ (pp 305–56), provides guidelines on methods of assessing permanent impairment involving the central nervous system. It is logically structured and consistent with the usual sequence of examination of the nervous system. Cerebral functions are discussed first, followed by the cranial nerves, station, gait and movement disorders, the upper extremities related to central impairment, the brain stem, the spinal cord and the peripheral nervous system, including neuromuscular junction and muscular system. A summary concludes the chapter.

5.2 Spinal cord injuries are to be assessed using AMA5Chapter 15. Table 15-6 (pp 396–97) is to be used for evaluation of spinal cord injuries. These impairments, once selected, are then combined with the corresponding additional spinal impairment from DRE categories II–V for cervical and lumbar impairment and categories II–IV for thoracic impairment to obtain an exact total value.

5.3 Impairments of the peripheral nervous system are assessed by using the relevant parts of the upper extremity, lower extremity and spine sections of AMA5.

The approach to assessment of permanent neurological impairment

5.4 AMA5 Chapter 13 disallows combination of cerebral impairments. However, for the purpose of the Guidelines, cerebral impairments should be evaluated and combined as follows:

• consciousness and awareness
• mental status, cognition and highest integrative function
• aphasia and communication disorders
• emotional and behavioural impairments.

The assessor should take care to be as specific as possible and not to double-rate the same impairment, particularly in the mental status and behavioural categories.

These impairments are to be combined using the Combined Values Chart (AMA5, pp 604–06). These impairments should then be combined with other neurological impairments indicated in AMA5 Table 13-1 (p 308).

5.5 AMA5 sections 13.5–13.6 (pp 336–40) should be used for cerebral, basal ganglia, cerebellar or brain stem impairments. This section, therefore, covers hemiplegia, monoplegia (arm or leg), and upper or lower limb impairment due to incoordination, or movement disorder due to brain injury.

5.6 If a person has a spinal injury with spinal cord or cauda equina, bilateral nerve root or lumbosacral plexus injury causing bowel, bladder and/or sexual dysfunction, he or she is assessed according to the method described in AMA5Section 15.7 and Table 15-6 (a)–(g) (pp 395–98).

5.7 Complex regional pain syndrome types 1 and 2 are to be assessed using the method in Chapter 17 of the Guidelines.

5.8 AMA5 Chapter 13, on the nervous system, lists many impairments where the range for the associated WPI is 0–9% or 0–14%. Where there is a range of impairment percentages listed, the assessor should nominate an impairment percentage based on the complete clinical circumstances revealed during the consultation, and in relation to all other available information.

Specific interpretation of AMA5

5.9 In assessing disturbances of mental status and integrative functioning; and emotional or behavioural disturbances; disturbances in the level of consciousness and awareness; disturbances of sleep and arousal function; and disorders of communication (AMA5 sections 13.3a, 13.3c, 13.3d, 13.3e and 13.3f; pp 309–311 and 317–327), the assessor should make ratings based on clinical assessment and the results of neuropsychometric testing, where available.

For traumatic brain injury, there should be evidence of a severe impact to the head, or that the injury involved a high-energy impact.

Clinical assessment must include at least one of the following:

• significant medically verified abnormalities in the Glasgow Coma Scale score
• significant medically verified duration of post-traumatic amnesia
• significant intracranial pathology on CT scan or MRI.

Neuropsychological testing should be conducted by a registered clinical neuropsychologist who is a member, or is eligible for membership, of the Australian Psychological Society’s College of Clinical Neuropsychology. Neuropsychological test data is to be considered in the context of the overall clinical history, examination and radiological findings, and not in isolation.

5.10 Assessment of arousal and sleep disorders (AMA5 Section 13.3c, pp 317–319): refers to assessment of primary sleep disorders following neurological injury. The assessor should make ratings of arousal and sleep disorders based on the clinical assessment that would normally have been done for clinically significant disorders of this type (ie sleep studies or similar tests).

5.11 Olfaction and taste: The assessor should use AMA5 Chapter 11, Section 11.4c (p 262) to assess olfaction and taste, for which a maximum of 5% WPI is allowable for total loss of either sense. The effect on activities of daily living should be considered.

5.12 Visual impairment assessment (AMA4 Chapter 8, pp 209–22): An ophthalmologist should assess all impairments of visual acuity, visual fields, extra-ocular movements or diplopia.

5.13 Trigeminal nerve assessment (AMA5, p 331): Sensory impairments of the trigeminal nerve should be assessed with reference to AMA5 Table 13-11 (p 331). The words ‘sensory loss or dysaesthesia’ should be added to the table after the words ‘neuralgic pain’ in each instance. Lesions of the ophthalmic division of the trigeminal nerve with impairment of corneal sensation should be apportioned with extra weighting.

If present, motor loss for the trigeminal nerve should be assessed in terms of its impact on mastication and deglutition (AMA5, p 262).

For bilateral injury to the trigeminal nerves, assess each side separately and combine the assessed WPIs.

5.14 Spinal accessory nerve: AMA5 provides insufficient reference to the spinal accessory nerve (cranial nerve XI). This nerve supplies the trapezius and sternomastoid muscles. For loss of use of the nerve to trapezius, the assessor should refer to AMA5 Chapter 16 on upper limb assessment, and a maximum of 10% impairment of the upper limb may be assigned. For additional loss of use of sternomastoid, a maximum of 3% upper limb impairment may be added.

5.15 Impairment of sexual function caused by severe traumatic brain injury is to be assessed using AMA5 Table 13-21 (p 342). For spinal cord, nerve root or more peripheral nerve injury, sexual impairment should only be assessed where there is appropriate objective evidence of spinal cord, cauda equina or bilateral nerve root dysfunction, or lumbosacral plexopathy.

5.16 Impairment due to miscellaneous peripheral nerves should be evaluated with reference to the following table.