Lecture Notes
Neurology in a Nutshell | Date 1/25/2025
Schedule (10:00 AM - 2:00 PM EST):
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10:05 AM - 10:55 AM Intervertebral Disc Disease (50 minutes)
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This session focuses on canine intervertebral disc disease (IVDD), a common cause of pain and myelopathy in dogs, and also occurring in cats. The session reviews neural localization, causes of pain, and the 2022 ACVIM consensus statement on thoracolumbar IVDD.
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Key concepts:
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Neurological exams are critical for creating differential diagnoses and treatment plans.
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The spinal cord is divided into segments: C1-C5, C6-T2, T3-L3, and L4-caudal, each with different clinical signs.
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Pain can result from issues affecting muscles, vertebrae, intervertebral discs, meninges, or nerve roots.
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IVDD is a common myelopathy in dogs, with disc degeneration predisposing to extrusion or protrusion.
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Type 1 IVDD involves extrusion of the nucleus pulposus, while type 2 involves protrusion.
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The modified Frankel scale is used to grade neurological deficits, with grade 5 indicating loss of pain sensation.
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Diagnostics include radiographs, MRI, CT, and myelogram. Radiographs can show narrowing, calcification, and mineralized material. MRI is highly sensitive, especially for peracute signs. CT is faster and less expensive but less accurate overall.
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Treatment can be medical (activity restriction and analgesia) or surgical (spinal cord decompression).
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Medical management is appropriate for ambulatory patients with pain. Surgery is indicated for non-ambulatory patients or those with severe neurological deficits.
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Timing of surgery is crucial for severe cases, ideally within 24 hours of losing pain sensation, although some dogs may recover ambulation even with delayed surgery.
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Post-operative pain management protocols are not standardized.
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11:00 AM - 11:50 AM Localizing, Diagnosing, and Managing Intracranial Disease (50 minutes)
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This session discusses how to localize lesions to different brain regions (prosencephalon, brainstem, cerebellum) to help create differential diagnoses and treatment plans.
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The brain is divided into the prosencephalon, midbrain, pons, medulla, and cerebellum.
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The midbrain, pons, and medulla make up the brainstem, also called the caudal fossa.
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Cranial nerves are associated with specific regions: I with the forebrain, II with the forebrain, III and IV with the midbrain, V with the pons, and VI-XII with the medulla.
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Key concepts:
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Localization is key to identifying the affected region and generating appropriate differentials.
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Ascending sensory pathways cross at the midbrain to the contralateral prosencephalon.
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Descending motor pathways start in the midbrain and are ipsilateral as they travel caudally.
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Seizures always localize to the prosencephalon.
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Caudal fossa lesions (midbrain, pons, medulla) cause ipsilateral deficits, including cranial nerve deficits (III-XII), upper motor neuron hemiparesis, proprioceptive ataxia, and posture reaction deficits.
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The reticular activating system, located in the caudal fossa, is responsible for mentation.
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The cerebellum is responsible for fine-tuning movements and inhibiting the vestibular system.
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Cerebellar dysfunction causes cerebellar ataxia, trunkal sway, and delayed and exaggerated postural reactions.
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Vestibular system maintains balance and coordinates head and eye movements. Vestibular dysfunction is characterized by head tilt, vestibular ataxia, nystagmus, and positional strabismus. Non-vestibular signs are used to localize within the system.
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Degenerative diseases of the brain are progressive and usually seen in younger patients. Storage disorders and cerebellar cortical degeneration (abiotrophy) are examples.
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Anomalous diseases are congenital or develop early in life. Hydrocephalus and cerebellar hypoplasia are examples.
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Metabolic diseases, like hepatic encephalopathy, electrolyte imbalances, and hypoglycemia, can cause encephalopathy.
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Neoplasia can be primary or metastatic. The most common primary brain tumors are meningiomas and gliomas. Hemangiosarcoma is the most common metastatic tumor in dogs.
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Infectious diseases can be viral, bacterial, fungal, protozoal, or parasitic.
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Immune-mediated diseases can cause multifocal encephalopathies.
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Trauma can cause contralateral prosencephalic or ipsilateral caudal fossa signs. Diencephalic and decerebellate rigidity are important postures to recognize.
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Toxic diseases can cause encephalopathy. Metronidazole can cause central vestibular or cerebellar signs. Ivermectin and bromethalin are also important toxins to consider.
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Vascular diseases like strokes are usually in the prosencephalon or cerebellum and can be ischemic or hemorrhagic.
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12:05 PM - 12:55 PM Chronic Seizure Management (50 minutes)
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This session focuses on the long-term management of seizures, including diagnosis, treatment, and monitoring. It is based on the 2015 ACVIM consensus statement.
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Key concepts:
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A seizure is a paroxysmal, synchronous discharge of neurons, resulting from too much excitatory or too little inhibitory activity in the brain.
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Seizures can be generalized or focal. Focal seizures with unilateral signs are due to a lesion on the contralateral side of the prosencephalon.
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Seizure events have pre-ictal, ictal, and post-ictal periods.
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Status epilepticus is a seizure lasting longer than 5 minutes, or more than two seizures within a short period without regaining consciousness.
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Seizures originate in the prosencephalon.
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Differentials for seizures include idiopathic epilepsy, intracranial, and extracranial causes.
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Idiopathic epilepsy is considered in patients between 6 months and 6 years old with normal interictal periods, a normal neuro exam, and ruled-out extracranial causes. An MRI and CSF tap can be considered but are not always required for diagnosis.
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Extracranial causes include toxins, metabolic, and nutritional diseases. Intracranial causes include vascular, infectious/inflammatory, traumatic, anomalous, neoplastic, and degenerative conditions.
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Lateralized neurological deficits indicate a structural brain issue.
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It's important to distinguish seizures from other conditions, including cardiac syncope and vestibular events.
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Diagnostic tests include a complete blood count, blood chemistry panel, urinalysis, and bile acids for suspected portal systemic shunts. An MRI and CSF tap are needed to investigate intracranial causes.
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Treatment with anticonvulsants is recommended if seizures occur monthly, every few months, are severe, or have a prolonged post-ictal period.
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Phenobarbital is a commonly used anticonvulsant. Monitoring includes drug levels at 2-6 weeks and then every 6 months, or 2 weeks after a dose change.
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Other medications include potassium bromide, zonisamide, and levetiracetam.
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Clients should keep a seizure calendar and seek emergency care for increased frequency, cluster seizures, or seizures lasting longer than 5 minutes.
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Brain tumors are a common cause of seizures in older dogs, especially brachycephalic breeds.
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Young puppies with seizures should be evaluated for metabolic, toxic, and anomalous conditions.
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Hypoglycemia should be identified because it is treated with dextrose, not benzodiazepines.
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Cats' seizures are more commonly due to primary diseases.
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CBD oil, ketogenic, and medium-chain triglyceride diets have variable results.
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1:00 PM - 1:50 PM Vestibular Dysfunction (50 minutes)
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This session covers the vestibular system's function, anatomy, localization, differential diagnoses, and management of vestibular dysfunction.
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The vestibular system is a sensory system involved in kinesthesia, maintaining body/head position, and coordinating eye movements.
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The system has three components: the peripheral (cranial nerve VIII), the central (vestibular nuclei in the rostromedulla and flocculonodular lobe of the cerebellum), and the caudal cerebellar peduncle.
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Dysfunction results in four hallmark signs: head tilt, vestibular ataxia, nystagmus, and positional strabismus.
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Key concepts:
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The vestibular system projects to various areas of the brain, including the medial longitudinal fasciculus, which coordinates eye and head movements.
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The cerebellum inhibits the ipsilateral vestibular nuclei.
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The vestibular system is bilaterally tonically active. A relative increase in activity on one side can be interpreted as a relative decrease on the other side.
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Loss of function in the peripheral vestibular system or the rostromedulla results in the four hallmark signs.
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Vestibular ataxia occurs due to a loss of excitation of ipsilateral extensors, causing the patient to fall/circle towards the affected side.
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The head tilt is toward the lesion. Spontaneous nystagmus occurs due to the brain interpreting a relative increase in activity from the unaffected side, causing the eyes to move away from the lesion. Positional strabismus occurs when the eye doesn't track with head movement.
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Localization within the vestibular system: Non-vestibular signs are used to determine peripheral, central, or paradoxical vestibular disease.
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Peripheral vestibular disease (inner ear or CN VIII lesion): Hallmark signs with horizontal (or rotary) nystagmus, ipsilateral CN VII deficits, and Horner's syndrome. Mentation and posture reactions are normal.
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Central vestibular disease (rostral medulla lesion): Hallmark signs with decreased mentation, proprioceptive ataxia, ipsilateral posture reaction deficits, tetraparesis, and cranial nerve deficits (V-XII). Nystagmus can be vertical.
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Paradoxical vestibular disease (cerebellar lesion): Hallmark signs with dysmetria/hypermetria on the side opposite the head tilt, and posture reaction deficits on the side opposite the head tilt.
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A flowchart is provided to aid in localization: identify vestibular dysfunction, evaluate posture reactions (normal = peripheral; deficits present = central or paradoxical); if deficits are present, determine if ipsilateral (central) or contralateral (paradoxical) to head tilt.
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Bilateral peripheral vestibular disease is characterized by wide head movements and a lack of physiologic nystagmus.
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Differentials for peripheral vestibular disease include congenital issues (rare), nasopharyngeal polyps (especially in cats), hypothyroidism, oral neoplasia, otitis media interna (most common), primary secretory otitis media (PSOM in Cavalier King Charles Spaniels), idiopathic vestibular disease, and ototoxicity.
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Differentials for central vestibular disease include storage diseases, hydrocephalus, hypothyroidism, brain tumors, thiamine deficiency, otogenic meningoencephalitis (direct extension of otitis media interna), viral causes (rabies, distemper, FIP), fungal causes (cryptococcus), non-infectious inflammatory diseases, trauma (rare), metronidazole toxicity, and vascular diseases (stroke to the rostral cerebellar artery).
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Otitis media interna is the most common cause of peripheral vestibular disease in dogs and cats. MRI can identify onogenic meningoencephalitis, an extension of otitis media interna to the brain stem.
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Idiopathic vestibular disease is the second most common cause of peripheral vestibular disease and is characterized by peracute onset.
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A stroke to the rostral cerebellar artery is a common cause of peracute, non-progressive paradoxical vestibular disease and is more common in older Greyhounds and Cavaliers.
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Severity of vestibular signs does not always correlate with prognosis.
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Early referral for MRI is recommended for most vestibular cases.