Peer reviewed The NeurologicNeurologic examiNatioNexamiNatioN in Companion Animals

In the January/February issue of Part 2: Interpreting Today’s Veterinary Practice, Part 1 of this article discussed performing Abnormal Findings a neurologic examination; Part 2 will address interpretation of Helena Rylander, DVM, Diplomate ACVIM () abnormal findings.

complete neurologic examination should be THE BRAIN done in all animals presenting with suspected Lesions in the brain can be localized to the: A neurologic disease. Abnormalities found during • Cerebrum and thalamus (ie, prosencephalon) the neurologic examination can reflect the location of • Brainstem the lesion, but not the cause, requiring further tests, • Cerebellum. such as blood analysis, electrodiagnostic tests, and In order to localize the lesion to a specific part of advanced imaging, to determine a diagnosis. the brain, an understanding of the anatomy and func- The neurologic examination evaluates different parts tion of the brain is necessary (see Brain Anatomy & of the nervous system; the findings from the examina- Related Functions). tion help localize the lesion to the: • Brain • Spinal cord A patient with ataxia may have a lesion in the proprio- • Peripheral nervous system ceptive pathways (peripheral nerves, spinal cord, or • Cauda equina. cerebrum), vestibular system, or cerebellum. Ataxia A fundic examination is recommended, especially in can be described as an uncoordinated gait, with cross- patients with brain disorders. Repeat neurologic exami- ing of the limbs and, sometimes, listing or falling to 1 nations are helpful to discover subtle abnormalities and or both sides. Ataxia can be further characterized as: assess progression of disease. • Proprioceptive: Mild, usually bilateral ataxia • Vestibular: Moderate, asymmetric ataxia • Cerebellar: Symmetric, . Read The Neurologic Examination Circling in Companion Animals—Part 1: The direction of circling is usually toward the side Performing the Examination (January/February with the lesion. The circles tend to be larger with le- 2013) at todaysveterinarypractice.com. sions in the prosencephalon than with lesions in the vestibular system.

40 Today’s Veterinary Practice March/April 2013 The NeuRologic exAmiNATioN iN comPANioN ANimAls, PART 2 |

Cranial Nerve Abnormalities Cranial nerve abnormalities are BRAIN ANAToMy & RElATED FuNCTIoNs signs of either a peripheral neu- Cerebrum & Thalamus ropathy or brainstem lesion. The cerebrum initiates movements; the thalamus executes movements. Brainstem lesions can be local- • A common finding in cats with a large meningioma compressing the ized to the part of the brain- cerebrum is difficulty initiating movements and continuous, aimless stem where the cranial nerve walking in large circles. nucleus is located. Peripheral • A patient with a thalamic lesion may have a compulsive behavior: if neuropathy may affect only 1 restrained, the patient may struggle, vocalize, and try to keep walking. nerve (eg, idiopathic facial pa- ralysis) or be part of a polyneu- Brainstem ropathy. The brainstem connects the cerebrum with the spinal cord and body. All information to and from the body (which is examined by postural reaction Decerebellate Posture assessment) passes through the brainstem and thalamus to leave or reach This rare posture is seen with a the cerebrum. severe lesion in the cerebellum. The brainstem includes the (mesencephalon), pons, and medulla Findings include: oblongata. localizing to one specific part of the brainstem is often not pos- • A mentally alert patient sible; however, cranial nerve deficits may help pinpoint the lesion. • Opisthotonus (dorsiflexion of The brainstem contains the cranial nerve cell bodies (except cN i and ii). the head and neck) • The midbrain contains the reflex center for vision and hearing (colliculi) • Increased extensor tone in and the nuclei of CN III and IV. the thoracic limbs due to • The pons lies between the midbrain and medulla oblongata and contains loss of inhibition from the the nucleus of CN V. in addition, some of the vestibular nuclei are partially cerebellum to the extensor in the pons. muscles • The medulla oblongata, the most caudal part of the brainstem, contains • Pelvic limbs with reduced the respiratory and blood pressure regulation centers, nuclei of CN VI to muscle tone that are usually XII, and the vestibular nuclei (4 vestibular nuclei on each side). flexed. Cerebellum Decerebrate Posture The cerebellum adjusts and moderates all movements initiated by the This rare posture is seen with cerebrum and executed by the thalamus. clinical signs that may indicate a a severe lesion in the midbrain cerebellar lesion include: or pons. • • The mentation in these • Variable and intermittent loss of the menace response patients is severely affected • ipsilateral postural reaction deficits and/or hypermetria (stupor or coma). • intention . • Opisthotonus may be present if the animal has a cerebel- lar lesion in addition to the brainstem lesion. • Increased extensor tone in all limbs is a result of loss of inhibitory function from the pontomedullary (RF or RAS), which affects extensor tone of the limbs.

Hemineglect (Hemiinatten- tion) Hemineglect is a reduced re- action to a stimulus (body or head) contralateral to a lesion in the cerebrum. To test for hemineglect observe the pa- tient’s reaction (turning the Lisa wirth, vMd head around, whining, trying Cross-section of cerebrum and thalamus and lateral aspect of brainstem to bite) while pinching the side

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of the trunk with hemostats. Compare reac- tions when pinching the other side.

Mental status Figure 1. Myotat- A change in mental status is caused by a lesion ic and withdraw- in the prosencephalon or brainstem (the re- al reflex pathways; ticular activating system is diffusely spread in thoracic and pel- the brainstem and responsible for our aware- vic limbs ness and arousability). • Owner’s knowledge of his or her pet’s Figure 2. C1 to C5 myelopathy: personality plus observations at home are 1 essential to assess the patient’s mental sta- Postural reactions tus, especially when there are subtle menta- are delayed or ab- tion changes. sent in all limbs • Repeat examinations and observation of the (red lines); spinal reflexes are nor- animal over a longer time period and in dif- mal or increased ferent surroundings are also helpful. (green lines)

Figure 3. T3 to L3 HoRNER’s syNDRoME & myelopathy: Pos- tural reactions and ANIsCoRIA spinal reflexes in Horner’s syndrome is caused by a 2 thoracic limbs are lack of sympathetic innervation to the normal; postur- eye. in patients with other neurologic al reactions are dysfunction, it is most commonly delayed or ab- seen with peripheral vestibular sent (red lines) dysfunction, c6 to T2 myelopathy, or but spinal reflex- brachial plexus injury (ie, outside the es are normal or spinal canal). clinical signs include: increased (green • Miosis (constricted pupil) lines) in pelvic • Enophthalmia (sunken eye) limbs • Ptosis (drooping eyelid) Figure 4. C6 to T2 • Protrusion of the third eyelid. 3 myelopathy: Pos- tural reactions are Anisocoria refers to pupils of delayed or absent unequal size. in all limbs; spi- • Loss of sympathetic tone (ie, nal reflexes are re- horner’s syndrome) results in one duced or absent in pupil failing to dilate (remaining thoracic limbs (red constricted) in darkness. lines) and normal • A parasympathetic lesion (ie, or increased in deficit of the oculomotor nerve pelvic limbs (green cNiii) results in one pupil failing to lines) constrict (remaining dilated) when 4 exposed to light. Figure 5. L4 to S3 myelopathy: • Brain edema and brain herniation Postural reac- may cause compression of the cNiii tions and spinal nucleus in the midbrain, resulting reflexes in thorac- in anisocoria, pinpoint pupils that ic limbs are nor- do not dilate in the dark or respond mal (green lines); to light, or fixed and dilated pupils. postural reactions in these patients mental status is are delayed or ab- also altered (stuporous or coma- sent and spinal re- tose). This is a serious finding that flexes are reduced requires immediate attention and or absent in pelvic treatment. 5 limbs (red lines)

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Paresis PosTuRAl REACTIoN AssEssMENT A patient with a cerebral lesion usually has mild, All postural reaction tests assess the sensory path- almost unnoticeable . Patients with brain- way from the paw to the brain stem and contralateral stem lesions have more pronounced paresis and cerebrum (through the limb and spinal cord) and the ataxia ipsilateral to the lesion. motor pathway that returns the same way to the paw (Figures A and B). conscious recognition is required from the cere- If there is a history of seizures, the lesion can be brum in order for the patient to replace the paw cor- localized to the prosencephalon, even if the neu- rectly; a slow or absent response indicates a problem rologic examination is normal. somewhere along the pathway. The pathways to and from the cerebellum contribute to the response and, THE sPINAl CoRD in patients with cerebellar lesions, cause altered pos- Patients with spinal cord lesions have normal tural reactions. mental status and cranial nerves. Spinal cord le- other findings help pinpoint the lesion to a spe- sions can be localized based on: cific area. • Gait abnormalities • In patients with brain disorders, postural reaction • Postural reaction deficits deficits are ipsilateral (both thoracic and pelvic • Spinal reflex abnormalities. limbs) to a lesion in the brainstem and contra- The spinal cord is divided into 4 functional lateral to a lesion in the cerebrum and thalamus (Figure C). regions: (1) C1 to C5, (2) C6 to T2, (3) T3 to L3, • A patient with a cervical myelopathy (C1–C5 or and (4) L4 to S3. • C6–T2) has postural reaction deficits in all limbs; A lesion in the C1 to C5 or C6 to T2 spi- a patient with a thoracolumbar myelopathy (T3–l3 nal cord segment results in tetraparesis and or l4–s3) or cauda equina syndrome has postural often postural reaction deficits in all limbs. reaction deficits only in the pelvic limbs. Sometimes the pelvic limbs are more affected than the thoracic limbs. • A lesion in the T3 to L3 or L4 to S3 spinal cord segment results in paraparesis and pos- tural reaction deficits in the pelvic limbs. The C6 to T2 and L4 to S3 spinal cord seg- ments are anatomically enlarged (thus, cervical and lumbar intumescences) because they contain the nerve cell bodies of the peripheral nerves to the limbs and tail. It is important to under- Figure A. Thoracic limb left (black) and right (blue) stand that these enlarged spinal cord segments postural reaction pathways are normal anatomy when evaluating images of the spinal cord.

sIgNs oF VEsTIBulAR sysTEM DysFuNCTIoN spontaneous nystagmus, vestibular ataxia, positional strabismus, head tilt, and circling are all signs of vestibular Figure B. Pelvic limb left (black) and right (blue) postural reaction pathways system dysfunction. The lesion may be in the inner ear or eighth cranial nerve (peripheral vestibular system) or in the brainstem or cerebellum (central vestibular system). Additional signs of brainstem dysfunction that are used to localize the lesion to the central vestibular system include: Figure C. With a left-sided brainstem lesion or right- • Ipsilateral postural reaction deficits sided cerebral lesion, postural reactions are affected in • Changes in mental status the left thoracic and pelvic limbs (red lines) but normal on the right side (green lines) • Deficits in other cranial nerves.

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In addition to postural reaction assessment, these pain, followed by paraparesis and postural reaction areas are also evaluated by testing the spinal reflex- deficits. es (Figure 1). • Later in the disease, reduced spinal reflexes to the • A lesion in the C1 to C5 or T3 to L3 spi- pelvic limbs, anus, and urinary sphincter are pres- nal cord segment results in normal (sometimes ent. increased) spinal reflexes (upper motor neuron • A history that includes slowly progressive parapa- signs) (Figures 2 and 3). resis (over many months) and pain on palpation of • A lesion in the C6 to T2 or L4 to S3 spinal the lumbosacral area can help localize a lesion to cord segment results in reduced muscle tone and the cauda equina. reduced spinal reflexes in the thoracic limbs (C6– T2) or pelvic limbs (L4–S3) (lower motor neuron FURTHER DIAGNOSIS signs) (Figures 4 and 5). Once the lesion is localized to a specific area of the nervous system, a list of differential diagnoses can Paresis be made. Based on lesion localization and differen- Tetraparesis without cranial nerve deficits or other tial diagnoses, appropriate diagnostic tests can be brainstem signs suggests a cervical myelopathy; para- chosen. n paresis is suggestive of a thoracolumbar myelopathy. Suggested Reading Schiff-Sherrington Posture DeLahunta A, Glass E (ed). The neurologic examination. This posture is seen with severe spinal cord injury be- Veterinary Neuroanatomy and Clinical Neurology, 3rd ed. tween the T3 and L4 spinal cord segments. There Philadelphia: WB Saunders, 2009, pp 487-501. is increased tone in the thoracic limbs, and normal or Dewey C. Functional and dysfunctional neuroanatomy: The reduced tone with of the pelvic limbs; the key to lesion localization. In Dewey C (ed): A Practical prognosis is guarded but not hopeless. Guide to Canine and Feline Neurology, 2nd ed. Ames, IA: The posture results from loss of normal inhibition Blackwell Publishing, 2003, pp 17-52. of the thoracic limb extensor muscle tone, which is Garosi L. Lesion localization and differential diagnosis. In normally controlled by the border cells in the lumbar Platt SR, Olby NJ (ed): BSAVA Manual of Canine and spinal cord. Axons of these cells ascend the spinal cord Feline Neurology, 3rd ed. Quedgeley, Gloucestershire, UK: BSAVA, 2004, pp 24-34. to reach the cervical intumescence, where they inhibit Lorenz MD, Kornegay JN. Localization of lesions in the ner- the thoracic limb extensor motor neurons. vous system. Handbook of Veterinary Neurology, 4th ed. Philadelphia: WB Saunders, 2004, pp 45-74. THE PERIPHERAL NERVOUS SYSTEM The peripheral nervous system includes the: • Neuromuscular system (peripheral motor nerves, muscles, and neuromuscular junctions) Helena Rylander, • Sensory nervous system DVM, Diplomate • Autonomic nervous system. ACVIM (Neurology), Peripheral nervous system diseases can be diffi- is a clinical assistant cult to diagnose, with signs of neurologic dysfunc- professor in the tion being vague or nonexistent. The following infor- Department of Medical mation does not pertain to diseases of the autonomic Sciences at University nervous system. of Wisconsin– • Patients with can have both Madison’s School of paresis and muscular weakness as well as exercise Veterinary Medicine. intolerance. Her clinical interests include spinal surgery, • Sometimes muscle pain is present. electrophysiology, and diagnostic imaging. • Postural reaction deficits and reduced spinal reflex- Dr. Rylander has published several articles es may be present. and a book chapter as well as presented • The history may reveal signs of neuromuscular at national and international meetings. disease, such as exercise intolerance, generalized She received her veterinary degree from weakness, voice change, and neurogenic muscle University of Agricultural Sciences in Uppsala, atrophy; these signs may be intermittent. Sweden. After 10 years in private practice in Sweden, Dr. Rylander completed a residency THE CAUDA EQUINA in neurology/neurosurgery at University The cauda equina are the spinal nerves (L6 –L7, S1– of California–Davis. She also completed S3, and Cd1–Cd5) caudal to the spinal cord in the the Educational Commission for Foreign lumbar vertebral canal. Veterinary Graduates (ECFVG) certification • Compression of the cauda equina initially results in program and received her DVM.

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