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Board Review Notes: Version: 3.0 Printed: Wed, Mar 1, 2017

The Neurological Examination: Goals = to confirm the presence of a neurologic disease and to localize it within the nervous system. The examination should be conducted in a logical, methodical, and consistent manner.

Major functional systems: consciousness, motor, nociception, proprioception (unconscious = muscle stretch, conscious = joint perception and position, special = balance and orientation to gravity), and the autonomic system. Major anatomic regions: cerebrum (including diencephalon), cerebellum, brainstem (including midbrain, pons and medulla), spinal cord, and peripheral nervous system.

Cerebrum = consciousness, voluntary motor regulation, pain localization, joint perception, vision, learning, behavior, and some cranial nerve response;

Cerebellum = muscle stretch perception, balance, and fine motor coordination;

Brain stem = consciousness, postural motor regulation, pain recognition, joint perception, muscle stretch perception, balance, the autonomic systems, and cranial nerve reflexes, and vegetative functions;

Spinal cord = motor regulation, pain perception, joint perception, muscle stretch perception, balance (cranial cervical cord), the autonomic system, and spinal reflexes;

Peripheral nervous system (PNS) is concerned with motor regulation, pain recognition, joint perception, muscle stretch perception, the autonomic systems, and reflexes.

  • General Observations: The general observations include: Mental status, Head Posture, Head Coordination, and the tendency to Circle.

Mental Status: Primarily cerebrum and brainstem.

Normal = alert (testing arousal) and aware of their surroundings (testing cognition and awareness). Awareness requires wakefulness, but wakefulness can be present without awareness.

Disorientation or Vertigo = Loss of Balance = Vestibular

Head Posture: Head is parallel to the ground and the neck is straight

  • Head tilt = . Vestibular disorders (usually towards the side of the lesion).

  • Torticollis (Twisted Neck): Vestibular or Cervical

  • Neck weakness = Feline Hypokalemic Polymyopathy, occipital dysplasia, botulism, cervical vertebral malformations and feline thiamin deficiency.

Head Coordination: Primarily cerebellum, some input from vestibular system.

  • Head tremor usually implies a cerebellar (or a cerebellar peduncle) lesion.

Circling: Brain diseases and vestibular injuries lead to circling.

Stance and Gait: Thoracic limbs at shoulder width and pelvic limbs at hip width; thoracic palmar aspect and pelvic plantar aspect in contact with the ground.

  • Abnormal stance may be due to weakness, loss of position sense, or pain.

Attitudinal and Postural Reactions: Test proprioceptive fibers of peripheral nerves, spinal cord, brain stem, cerebrum, and cerebellum. Some test special proprioception. Also test the UMN’s and the Lower Motor Neurons (LMN).

Cranial Nerve Examination: (See Table)

Spinal Segmental Reflexes: See Table

NOCICEPTIVE EVALUATION:

Diminished Pain perception. Identifies Severity of Injury, May help localize

Exaggerated Responsiveness to Pain. Localize extramedullary injury

CEREBRAL DISORDERS tend to cause changes in mental status, vision, and cause seizures. Many patients with cerebral diseases will circle (without a head tilt). Most patients with cerebral diseases have weakness of limbs, with increased spinal reflexes and decreased postural reactions.

CEREBELLAR DISORDERS tend to cause ataxia of head and limbs. These patients may have tremor of the head, as well as postural tremor of the trunk when the patient is standing. Many patients with cerebellar diseases will have head tilts and pathologic nystagmus. If the lesion involves the cerebellar peduncles, the patient may also have torticollis.

BRAINSTEM DISORDERS tend to cause cranial nerve deficits and weakness of limbs. Most brainstem disorders cause vestibular signs. Rostral brain stem lesions often depress consciousness. Caudal brain stem lesions often result in an abnormal heart rate and rhythm or respiratory distress.

SPINAL CORD DISORDERS tend to cause weakness and ataxia of limbs.

  • The only cranial nerve deficit would be Horner’s syndrome. It may be seen with a lesion from C1- T2, but is most common with lesions of C8 -T2.

  • Spinal cord disorders are a common neurologic cause of urine/fecal incontinence.

PERIPHERAL NERVE DISORDERS may be either focal or generalized.

  • Focal disorders may involve a single nerve root (e.g. Facial Paralysis) or a collection of nerve roots (e.g. Cauda equina syndrome or brachial plexus nerve root avulsion). Focal injuries of spinal nerves are usually due to trauma or neoplasms. Focal injuries of cranial nerves are frequently idiopathic (e.g. Facial paralysis or trigeminal neuritis), but may be due to trauma and tumors as well.

  • Generalized disorders may be limited to the spinal nerves or involve all nerves. Usually, they are motor and/or sensory. In some cases (e.g. Botulism) they may involve the autonomic system and in rare cases (pan-dysautonomia of cats/dogs) may be primarily confined to the autonomic nervous system. Generalized LMN disorders are usually the result of inflammatory/immune (e.g. Myasthenia gravis or Acute Idiopathic Polyradiculoneuritis - Coonhound paralysis); metabolic/endocrine (hypothyroid neuromyopathy); or toxic disorders (botulism, tick paralysis).

TRAUMA: This remains the single most common cause of nervous system dysfunction. It may affect any part of the NS and be focal or generalized.

Etiologies: HBC, Disc Extrusions, Cervical Instabilities, etc.

Primary Events: Occur at time of injury, are primarily mechanical, e.g. fiber tracts are mechanically disrupted and cell membranes injured.

  • May not be reparable.

  • Severity depends on force of trauma.

  • Recovery depends on severity, location, appropriate treatment

Intracranial Trauma

  • Secondary Events:

Pressure Changes: ICP rises in most patients with Head trauma. This decreases cerebral blood flow. Intracranial blood volume may increase due to venodilation.

Edema: Cytotoxic edema accumulates in cells, particularly neurons and astrocytes and usually arises from cellular hypoxia. Vasogenic edema is extracellular and arises from leakage across a damaged BBB. Vasogenic edema primarily affects white matter and is more amenable to therapy than cytotoxic.

Hypoxia: Usually a consequence of elevated ICP. Hypercarbia further elevates ICP.

Seizures: seizures may be immediate or delayed sequela to trauma.

Therapeutic Approach:

Elevate the head to minimize blood pooling in CNS and facilitate CSF flow.

Oxygen lowers CO2, lowering ICP. Oxygen also acts to prevent or reverse cerebral edema.

Steroids reduce edema and stabilize cell membranes. Steroids also stabilize the BBB, preventing further edema from developing. Steroids decrease the inflammatory response that results from tissue necrosis.

Diuretics: osmotic diuretics (e.g. mannitol), carbonic anhydrase inhibitors, and furosemide all decrease brain edema. Furosemide appears to decrease the production of CSF and facilitate resorption of brain edema. The clinical effects are lengthened and the potential for rebound edema is lessened when furosemide and mannitol are given together.

Stabilization: If spinal fractures/luxations/instability is present - repetitive trauma will occur - stabilization is required

Decompression: If external mass effect, e.g. disc, then decompression is generally needed.

VASCULAR DISORDERS: Nervous system vascular injury may result from a variety of causes, including: neoplasms, CNS infection, aneurysms, atherosclerosis, Arterio-Venous malformations, cardiogenic emboli, vasospasm, atrial fibrillation, mitral stenosis, hematologic disorder, vasculitis (secondary to parvoviral infection or Rocky Mountain Spotted Fever). Other causes of neurovascular disease include: polycythemia, hyperviscosity syndromes (Plasma cell myeloma, Macroglobulinemia), bleeding disorders, immune disease, uremia, sepsis, Disseminated Intravascular Coagulation (DIC), vascular tumors, and cardiomyopathy. Most reported intracranial vascular injuries are associated with a systemic illness such as sepsis, hypothyroidism, bleeding disorders, or septicemia. Ischemic and hemorrhagic events appear to occur with about equal frequency.

ABERRANT PARASITE MIGRATION: A number of metazoan parasites may localize in the CNS as part of aberrant migration. Most commonly found are Paralophystrongylus tenuis (goats & llamas), Dirofilaria immitis and Cuterebra. Other parasites include Toxascara, Ancylostoma, Taenia, and Angiostrongylus. The signs are referable to the portion of CNS involved, focal and progressive. Esosinophils are usually seen in CSF. A definitive diagnosis rests on necropsy. Therapy is directed both at inflammation (steroids) and underlying etiology (anthelmintics) - therapy is ineffective in many cases. Probably the most common cause of spinal cord disease in goats and llamas.

EPILEPSY: An epileptic seizure is the clinical manifestation of excessive and/or hypersynchronous, abnormal neuronal activity in the cerebral cortex. If no underlying cause for the seizure can be identified, then the epileptic seizures are defined as Primary Epileptic Seizures (idiopathic or cryptogenic). Primary genetic epilepsy (breed related inherited epilepsy) has been documented in beagles, German shepherds, Keeshounds, and Malinois. No inherited epilepsy has been proven in cats. Epileptic seizures resulting from structural cerebral pathology are defined as Symptomatic Epileptic Seizures. If a patient has a chronic brain disorder characterized by recurrent epileptic seizures (PES or SES), then that patient has epilepsy.

Seizures have three components. The aura is the initial manifestation of a seizure. The ictal period is the actual seizure event manifested by involuntary muscle tone or movement, and/or abnormal sensations or behavior lasting usually from seconds to minutes. Following the ictus is the post-ictal period.

Seizures can be partial or generalized. Partial seizures are the manifestation of a focal epileptogenic event in the cerebral cortex, think symptomatic. Generalized seizures are subdivided into convulsive ("grand mal") and non-convulsive ("petit mal") seizures. Generalized convulsive seizures are the most common seizure type seen in veterinary medicine.

Diagnostic Approach

LESS THAN 1 YEAR OF AGE Developmental, Inflammatory, Idiopathic

BETWEEN 1-5 YEARS OF AGE Idiopathic, Inflammatory, Metabolic,

Nutritional, Trauma, Vascular, Toxic,

Developmental,

FIVE YEARS OF AGE OR OLDER Neoplastic, Inflammatory, Trauma, Metabolic, Idiopathic, Degenerative, Toxic

Initiate antiepileptic therapy based on etiology, seizure type and frequency. Treatment goals are to:

  • use one drug,

  • obtain a desired clinical outcome,

  • and have the fewest adverse effects.

Phenobarbital (PB) is currently the antiepileptic drug of choice in dogs. Other antiepileptic drugs are either too hepatotoxic (Dilantin®/Primidone®), have very rapid elimination half-lives (Dilantin®, carbamazepine) or not well studied. Bromide (usually as the potassium salt) is being extensively studied and is now the second choice drug, either in combination with phenobarbital or by itself. Diazepam remains effective in cats. Diazepam cannot be used long term in dogs due to resistance/tolerance developing to its anticonvulsant effects.