UMEM Educational Pearls - Neurology

• Infections induce activated T cells and antibodies, which within the context of an influenza syndrome, are thought to cross react with axonal antigens and macrophages, resulting in demyelination.  This process likely triggers a subsequent Guillain-Barre’ syndrome (GBS).

• Presumably, influenza vaccine induces a similar response in susceptible individuals.

• Juurlink and colleagues found there to be a 1.45 relative risk, which equals a 1.7-fold adjusted relative risk for contracting GBS, associated with influenza vaccination.

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• In 1976, vaccination with the swine flu vaccine was associated with a small risk of developing Guillain Barre Syndrome (GBS), approximately 1 additional case per 100,000 people who received the swine flu vaccine, which was slightly higher than the background rate for GBS.

• Since then, numerous studies have been done to evaluate if other flu vaccines were associated with GBS. In most studies, no association was found, but two studies suggested that approximately 1 additional person out of 1 million vaccinated people may be at risk for GBS associated with the seasonal influenza vaccine.

• It is important to keep in mind that severe illness and possible death can be associated with influenza, and that vaccination is the best way to prevent influenza infection and its complications.

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• Guillain-Barre’ Syndrome (GBS) is a group of immune mediated processes characterized by motor, sensory, and autonomic dysfunction of peripheral nerves.

• Classically, GBS is an acute inflammatory demyelinating polyneuropathy (AIDP) consisting of progressive, symmetric, ascending muscle weakness and paralysis, associated with diminished deep tendon reflexes.

• This rare condition, affecting 3,000 to 6,000 Americans annually (1 to 2 out of 100,00 per year), can lead to respiratory failure in severe cases, requiring vigilance in pro-actively administering mechanical ventilation as needed.

• Pregnant patients presenting with their first seizure, should essentially be managed in the same way as any other adult patient (i.e. Is the source of the seizure due to a reversible systemic condition, and if not, is the patient at risk for recurrent unprovoked seizures; specialist follow-up arrangement).

• Additional pregnancy-related conditions that can be associated with seizure, such as eclampsia and cerebral venous thrombosis, should be considered.

• While the safety of all anti-epileptic drugs in pregnancy is questionable, the use of valproate (Depakote) should definitely be avoided, given its compelling association with fetal malformations.

• Strokes resulting from embolic or thrombic insult to the middle cerebral artery (MCA) are common.

• These patients tend to present with contralateral motor deficit which is most pronounced in the upper extremity (and face), compared to the lower extremity.

• If motor weakness is more pronounced in the lower extremity, consider an anterior cerebral artery (ACA) infarct as the source.

• Should patients continue to seize even after administration of a benzodiazepine (i.e. lorazepam, diazepam) plus phenytoin, additional high-dose phenytoin should first be considered.

• While the standard loading dose for IV phenytoin is 10-20 mg/kg, it is recomended that up to 30 mg/kg of phenytoin be given for refractory status epilepticus prior to using another anti-epileptic, such as phenobarbital, pentobarbital infusion, or propofol infusion.

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• Indications and timing of head CT scans in patients with a first-time seizure (FTS), who have returned to a normal baseline, are controversial.

• The range of such patients with abnormal head CT's is broad, at 3 to 41%.
   
• A retrospective study found that 22% of patients with a FTS and normal neurologic exams, had an abnormal head CT (Hennemen, et al).

• Another study found that in patients with suspected alcohol withdrawal seizures, 58% had an abnormal head CT, 16% of which were clinically significant findings (Earnest, et al).

• When feasible, neuroimaging of the brains of patients presenting with a FTS should be performed in the emergency department.  Deferred outpatient neuroimaging may be used when reliable follow-up is ensured. (Level B Recommendation).

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• The classic triad of fever, meningismus (stiff neck), and altered mental status only occurs in 44% of cases of acute bacterial meningitis (ABM).

• Headache is a much more common presenting complaint with ABM.

• The sensitivity and specificity of Kernig and Brudzinski signs are suboptimal, making their presence or absence of little diagnostic value.

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The following symptoms of phenytoin toxicity typically present initially, once plasma concentrations reach the listed levels below:

• Nystagmus (on lateral gaze, at 20 mcg/mL)
• Ataxia (at 30 mcg/mL)
• Dysarthria and lethargy (at over 40 mcg/mL)

Other associated symptoms include tremor, hyper-reflexia, nausea, and vomiting.

• The therapeutic ranges for phenytoin (dilantin) and phenobarbital in adults are 10 to 20 mcg/mL and 10 to 30 mcg/mL, respectively.

• Phenytoin plasma levels rise more rapidly than phenobarbital levels; therefore, an acute overdose of the two together will likely manifest as phenytoin toxicity before phenobarbital toxicity.

• Phenytoin has a more narrow margin between therapeutic and toxic levels than does phenobarbital.

• Glucose abnormalities and hyponatremia are the two laboratory findings most frequently associated with triggering first-time seizures in adult patients.

• Always check an HCG in women who present with their first seizure, as this may reveal the source (i.e. eclampsia) and/or may affect testing, disposition, and initiation of an anti-epileptic drug (AED).

• Drug abuse screens should be considered in patients with their first seizure, but no prospective studies have demonstrated benefit from routine use.

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• To be conscious, one must be both awake and alert.

• Patients who sustain severe anoxic cortical damage, with brainstem sparing, exhibit wakefulness and sleep, but are not aware, and thus, are unconscious.

• This description is the hallmark of a "vegetative state."

• A coma is a deep depression in the state of altered level of consciousness, which is characterized by the patient's response to verbal or painful stimuli.
  

Depending on the location of infarct, stroke patients with dysarthria (a motor speech disorder) may exhibit the following signs and symptoms:

• "Slurred" speech
• Speaking softly or barely able to whisper
• Slow rate of speech
• Rapid rate of speech with a "mumbling" quality
• Limited tongue, lip, and jaw movement
• Abnormal intonation (rhythm) when speaking
• Changes in vocal quality ("nasal" speech or sounding "stuffy")
• Hoarseness
• Breathiness
• Drooling or poor control of saliva
• Chewing and swallowing difficulty

• Progressive Multifocal Leukoencephalopathy (PML) is a life-threatening demyelinating condition that results from the reactivation of the polyomavirus JC. It primarily affects the immunocompromised (most commonly individuals with CD4 counts of < 200).

• Prior to the advent and widespread use of anti-retroviral therapy, 1 to 5% of those with AIDS developed PML.  HAART is now considered a mainstay of treatment, along with cessation of immunosupressant therapies.

• PML lesions typically occur bilaterally in the peri-ventricular white matter portions of the brain and do not conform to specific cerebrovascular territories. 

• Non-contrast CT and MRI may reveal PML lesions, but definitive diagnosis is made via brain biopsy. 

• Symptoms of PML include subacute neurologic deficits such as:  mental status abnormality, gait ataxia, limb ataxia, hemiparesis, monoparesis, and visual abnormalities such as diplopia and hemianopia.  Seizure occurs in up to 18% of cases.   

• Lidocaine toxicity typically manifests as central nervous system symptoms such as tongue numbness, tinnitus, visual disturbances, seizure, and cardiovascular depression.

• The maximum dose of lidocaine without epinephrine is 5 mg/kg (4.5 mg/kg, to be exact) and 7 mg/kg for lidocaine with epinephrine.  The total maxiumum dose is 300 mg.

• During the emergency department management of all stroke patients, an NPO (nothing by mouth) status should be maintained until a formal swallow study can be performed to determine whether there is dysphagia.

• The best predictor of dysphagia (swallowing difficulty) in a stroke patient is the presence of dysarthria (motor speech abnormality).

• While the absence of a gag reflex, may suggest some degree of dysphagia, remember that about 10 to 15% of people lack a gag reflex.

• Dysarthria is a motor speech abnormality that commonly results from stroke and is related to focal muscular deficits in the face.

• One of the most challenging aspects of recognizing dysarthria relates to distinguishing it from apraxia. 

• Apraxia has nothing to do with a focal motor deficit, but rather a cortical deficit which results in an inability to optimally execute the function of the facial musculature.

• Isolated dysarthria without other neurologic deficit, termed pure dysarthria, is rare and thought to result from multiple lacunar infarcts causing hypoperfusion of the frontal cortex.

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• While most typically only test and document that "cranial nerves II - XII are intact" when examining a patient, I would argue that cranial nerve I should also be tested in all head injury cases wherein there was significant facial/nasal trauma
• Direct blows to the face, by way of airbag deployment, dash board trauma, or assault, for example, can easily cause the ethmoid bone (see image below) to fracture leaving the olfactory nerve exposed to potential trauma as it crosses the cribiform plate.
• Shearing of this nerve can cause irreversible anosmia or hyposmia (inability or decreased ability to smell, respectively).
• The easiest, most effective way to test cranial nerve I is one nostril at a time (occlude the one not being tested), using items such as coffee, peppermint oil, or cloves.  More annoying smells like that of an alcohol prep or benzoin, can also be used and would likely be more readily accessible in an emergency department.