Name the 12 cranial nerves.
- CNI: olfactory (smell)
- CNII: optic (vision)
- CNIII: occulomotor (EOM)
- CNIV: trochlear (EOM)
- CNV: trigeminal (touch, pain, jaw muscles)
- CNVI: abducens (EOM)
- CNVII: facial (muscles of expression, taste)
- CNVIII: auditory (hearing, balance)
- CNIX: glossopharyngeal (taste, muscles of throat and larynx)
- CNX: vagus (internal organs)
- CNXI: spinal accessory (neck muscles)
- CNXII: hypoglossal (tongue movements)
Which cranial nerves are purely sensory?
Which cranial nerves are purely motor?
- CN III
- CN IV
- CN VI
- CN XI
- CN XII
Which cranial nerves have mixed function (sensory and motor)?
What are neurons and what provides their blood supply?
- individual cells bundled inside perineurium to make a nerve
- vaso nervorum
- Note: they are only ever ascending or descending (one way streets)
Part of the action potential has Na concentrated outside of the cell and K concentrated inside the cell with gated channels preventing movement, keeping the membrane potential at -70mV.
resting (resting membrane potential)
Part of the action potential where Na gated channels open which results in an influx of Na into the cell, and the membrane potential becomes +30mV. What medications affect this process?
- lidocaine/marcaine (Na channel blockers)
Part of the action potential where K channels open (triggered by membrane potential), allowing K to move out of the cell as the Na channels close.
- Note: hyper polarization prevents repeated stimuli until corrected
Point of no return for an action potential, analogous to squeezing the trigger.
Defined as once the action potential starts it continues in a steady wave all the way down the axon until it reaches the nerve terminal.
How are electrical impulses carried in myelinated nerves and why is this important? What disease causes demyelination resulting in a life threatening condition?
- voltage gated channels are only present at nodes of Ranvier which results in increased speed of transmission with less energy
- Guillan Barre syndrome
What is the process of impulse transmission across the synapse?
- nerve impulse arrives causing influx of calcium
- calcium causes release of neurotransmitters
- neurotransmitters diffuse across synapse
- binding of NT to membrane protein causes voltage change on the postsynaptic membrane
- NT is broken down
What is temporal summation?
many stimuli in close sequence (i.e. loud sound, pain, bright lights)
What is spatial summation?
many stimuli occurring at the same time
What is the main difference between depolarization and hyperpolarization?
- open sodium gates will depolarize
- open potassium gates will hyperpolarize (turns nerve off)
Methods of testing nerve function that is performed by a neurologist or PMR to evaluate for neuromuscular disorder, peripheral neuropathy or entrapment.
- EMG: records intrinsic electrical activity within muscle
- NCV: stimulates a nerve at one point and records response
What are metabolic disorders that can cause polyneuropathy?
- B12 deficiency: presents as distal, symmetric sensorimotor polyneuropathy
- ETOH abuse: another distal, symmetric sensorimotor polyneuropathy
- diabetes (peripheral neuropathies)
What are infectious diseases that can cause polyneuropathy?
- leprosy: most common worldwide cause of treatable neuropathy
What are inflammatory disorders that can cause polyneuropathy?
- multiple sclerosis
- Guillan Barre syndrome
What can cause isolated peripheral neuropathy?
- compressive disorder/issue
- traumatic event
What are examples of mononeuropathy?
- isolated peripheral neuropathy (compressive, traumatic)
- Bell's palsy (facial nerve palsy)
- trigeminal neuralgia
Isolated peripheral neuropathy due to compression of the radial nerve as it spirals around the humerus. Presents with wrist drop, inability to extend at the elbow and wrist, numbness of the back of hand and wrist, lost triceps reflex. Most commonly occurs when a person falls asleep with their arm thrown over the back of a chair.
- radial (C5-C8)
- aka "saturday night palsy" which refers to nerve damage that happens if a drunk person falls asleep with the their arms compressed by a bar edge
Isolated peripheral neuropathy causing impaired wrist and finger flexion and radial deviation of the hand, atrophy of thenar eminence, loss of sensation over the palmar aspect of the index and middle fingers.
- median (C6-T1)
- aka carpal tunnel syndrome
Isolated peripheral neuropathy resulting from compression at the groove between the olecranon process and medial humeral epicondyle (interossei weakness after fracture-"newspaper sign"). Pt can't perform ulnar deviation of the hand, and loses sensation over the pinky finger.
Isolated peripheral neuropathy that causes pain over the anterior lateral aspect of the thigh.
lateral femoral cutaneous nerve (Meralgia paresthetica)
Isolated peripheral neuropathy due to nerve becoming entrapped with anterior tibial compartment syndrome following exercise, trauma, vascular occlusion (can't evert/dorsiflex foot). Pt presents with foot drop and high slapping gait and sensory loss between big and second toes.
- deep peroneal
- Note: requires immediate surgical decompression
Isolated peripheral neuropathy due to nerve entrapment below and behind the medial malleolus (ankle sprain) that causes paresthesias along the plantar aspect of the foot. Can be misdiagnosed as plantar fasciitis, Morton's neuroma, etc.
posterior tibial nerve (tarsal tunnel syndrome)
Causes a macrocytic anemia, macro-ovalocytes, and hypersegmented neutrophils on smear. Rare due to it being found in lots of plants and animal, and usually only occurs in alcoholics, vegans and post gastrectomy pts. Rarely caused by fish tapeworm, pancreatic insufficiency or Crohn's disease.
vitamin B12 (cobalamin) deficiency
Neurologic involvement with this issue is usually complex in nature but tends to affect the peripheral nerves first. Paresthesias are the primary patient problem, followed by posterior column issues which lead to balance disturbances and dementia or other neuropsychiatric changes in advanced cases.
vitamin B12 (cobalamin) deficiency
What does the physical exam reveal in a pt with vitamin B12 deficiency?
- decreased vibratory sensation
- loss of position sense
What are normal B12 levels? What are the levels in patients with overt deficiency and patients who are symptomatic?
- normal: >240 pg/mL
- overt: <170 pg/mL
- symptomatic: <100 pg/mL
What is the other most common cause besides B12 deficiency for megaloblastic anemia?
folic acid deficiency
How is vitamin B12 deficiency treated and how long does the patient need to be treated? When are symptoms still reversible?
- IM injections with 100mcg x 1wk, the weekly for first month, then monthly FOR LIFE
- reversible if symptoms are present <6 months
Blood alcohol levels less than _____ rarely cause any significant motor abnormalities. What is the legal limit for DUI? What levels are lethal?
- 50 mg/dL
- 80 mg/dL
- 350-900 mg/dL
How is intoxication manifested? What is the BAL of a person exhibiting these signs?
- ataxia, dysarthria, N/V
- BAL >150 mg/dL
An encephalopathy characterized by erratic behavior, memory and recall problems as well as emotional instability. May be associated with Wernicke-Korsakoff syndrome.
chronic alcoholic brain syndrome
Primary findings of this disease include macular/nodule skin lesion that can be pale or erythematous, present with superficial nerve thickenings that are anesthetic, is usually associated with exposure in an endemic area and is caused by an acid fast bacilli that can be found in nasal scrapings or skin lesions of affected patients.
leprosy (Hansen disease)
What are the signs and symptoms of leprosy (Hansen disease)?
- insidious onset
- effects cooler skin areas
- neurologic disruptions (directly related to nerve infiltration & thickening causing anesthesia and motor abnormalities)
What are the two distinct presentations of leprosy (Hansen disease)?
- lepromatous (multibacillary): defective immune system, more progressive, symmetric nerve involvement, multiple bacteria
- tuberculoid (paucibacillary): intact immune system, more benign, asymmetric nerve involvement, fewer bacteria present
What are the differential diagnoses of leprosy (Hansen disease)?
- erythema nodosum & multiforme
- cutaneous TB
What are some complications that can arise with leprosy (Hansen disease)?
- motor abnormalities
- kidney failure
- secondary amyloidosis
How is leprosy (Hansen disease) treated?
- lepromatous: rifampin 600mg once a month, dapsone 100mg QF, clofazimine 300mg once a month then 50 mg daily for 12 months
- tuberculoid: rifampin 600mg once a month and dapsone 100mg for 6 months
Reactivation of the varicella virus, "lives" in dorsal root ganglion and causes severe pain that may preceded appearance of a rash with lesions similar to chickenpox.
herpes zoster AKA "shingles"
How is herpes zoster (shingles) treated?
- acyclovir or valcyclovir if caught early (within 48 hours) can lessen the course
- corticosteroids reduce duración & severity of acute eruption
How is post herpetic neuralgia that persists for many months after herpes zoster (shingles) treated?
Also known as acute inflammatory polyradiculoneuropathy that may follow an illness or vaccination that causes immunologic demyelination. Is associated with preceding campylobacter jejuni enteritis.
What are the signs and symptoms of Guillain-Barre syndrome?
- variable weakness (main complaint) usually in legs that ascends
- no pain
- DTRs usually absent
- may progress to muscles of respiration/swallowing
- autonomic dysfunction (tachycardia, arrhythmias, hypotension, pulmonary dysfunction, loss of sphincter control, sweating, labile BP)
How is Guillain-Barre evaluated for and treated?
- CSF: high protein, normal cell count
- NCV: slowing/motor and sensory conduction (demyelination pattern)
- Treatment: hospital (ICU +/- intubation), IV immunoglobulin, plasmapheresis, steroids not helpful
What is the prognosis for patients with Guillain-Barre syndrome?
- self limiting disorder that ends progression by about 4 weeks
- 75% recover completely within a few months to a year (areflexia may persist)
- 5-10% recover with severe disability or have one or more late relapses (chronic inflammatory demyelinating polyneuropathy/ CIDP)
- death rate is 2-3%
Nerve death related to long-standing hyperglycemia, ischemic in nature and usually seen in non-compliant patients. Primary affects sensory and autonomic nerves.
- diabetic neuropathy
- Note: 3rd-5th decades for type 1, >50 yrs for type 2
- Note2: rarely have just one type, sensory often associated with terrible pain, peripheral nerves are often symmetric, truncal results from one or more intercostal/lumbar nerve and coexists with neuropathy of the legs
What is often manifested with diabetic neuropathy that affects motor nerves (motor neuropathy)?
- muscles innervated by the obturator nerve (quadriceps femoris, illiopsoas, adductor magnus)
- ipsilateral loss of knee jerk
What are examples of autonomic neuropathy in diabetic peripheral neuropathy?
- vasomotor disturbance in the limbs (orthostatic HOTN)
- sweating disturbance
- CV (exercise intolerance, dizziness)
- GI (gastric atony/gastroparesis)
- GU (bladder dysfunction, ED)
- hypoglycemia unawareness
In what percentage of diabetics are peripheral neuropathies manifested? When should neuropathies be suspected in these patients? When do autonomic neuropathy symptoms tend to begin?
- suspected in all DM2 and pts with DM1 for more than 5 years
- develops in pts with DM for more than 20 years with poor glycemic control
How is diabetic neuropathy treated?
- tight glycemic control (A1C <6.5%) is best
- pain control with….
- simple analgesics (narcs, NSAIDs)
- capsaicin cream (substance P)
- amitriptyline (50mg po qhs)
- gabapentin (300mg po TID)
- duloxetine (60mg po qd)
- tramadol (50mg po q6h prn)
What are the preventative measures for diabetic neuropathy?
- pt education regarding proper foot care, wear, and checking feet daily
- annual foot exam with monofilament testing
- annual dilated eye exam (DM retinopathy)
What are disorders of the NMJ and muscle?
- myasthenia gravis
- muscular dystrophy
What are the characteristics for neuromuscular-transmission disorders?
- normal/reduced muscle tone
- normal/depressed DTRs and superficial reflexes
- no sensory changes
- patchy weakness conforming to the distribution of any single anatomic structure
- frequently involves cranial muscles and may fluctuate in severity over short periods esp with activity
Toxin exposure from contaminated wounds. In the extremities the toxin is transported retrograde into the spinal cord along the motor nerves. If the wounds are in the face or head, access is through the brainstem to the motor nerves. It can also gain access to skeletal muscle through the bloodstream, and from there the toxin can gain access to the motor nerves.
tetanus (clostridium tetani) "lock jaw"
In the spine and brainstem this toxin will interfere with the release of GABA (inhibitory NT), which results in nerve hyperactivity leading to increased muscle tone, spasms, and rigidity. It primarily affects the motor nerves but it can also cause some disinhibition to the autonomic nerves as well. Fatality rate is up to 60%.
tetanus (clostridium tetani) "lock jaw"
Disease that incubates for about two weeks that can lead to trismus, dysphagia and laryngeal spasm (potentially life threatening), facial muscle contortion (risus sardonicus), painful muscle spasm and rigidity that can progress and affect both axial and limb musculature and lead to opisthotonis (hyperextended posturing), and continuous motor activity or absence of normal silent period in the masseter muscle reflex.
tetanus (clostridium tetani) "lock jaw"
What is the immunization schedule for tetanus?
- 3 doses in children at 1 month intervals with a yearly booster
- same for adults but the third dose is delayed for at least 6 months (no fourth dose)
- lasts 5-10 years
When is risk of infection with tetanus moderate?
- wound penetrates muscle
- associated with wood/pavement
- human bites
- non-abdominal bullet wound
When is risk of infection with tetanus high?
- if acquired in a barnyard
- near a sewer or waste material
- abdominal bullet wounds
Caused by toxin that prevents the release of ACh at the NMJ and can cause neuromuscular paralysis. Can be food or wound borne (most commonly from canned foods). Results in weakness about 12-72 hours after ingestion.
What are the signs and symptoms of weakness as a result of botulism?
- double/blurred vision
- eye lid lag (ptosis)
- facial weakness
- nasal speech
- difficulty with respirations
- limb weakness (last sign)
What signs could point to botulism as a consideration in a child less than one year?
- poor feeding
- failure to thrive with progressive weakness, impaired respiration
- normal reflexes, no sensory deficits
What is the relation to the dose of toxin and latent period to the risk of infection and adverse outcome?
the shorter the latent period to onset of sx, the greater the dose of toxin and greater the risk of infection and adverse outcome
How is the diagnosis of botulism made?
- lab confirmation through botulism toxin in serum or stool or the food most recently consumed
- Note: most common types are A, B, and E
How is botulism treated?
- supportive care initially
- hospitalization with/without ventilator support
- trivalent antitoxin (if pt is not allergic to horse serum)
- guanidine hyodrochloride 25-50mg/kg/d in divided doses (facilitates ACh release, may improve muscle strength)
NMJ weakness due to decreased ACh receptors, is immune mediated. Patient reports fluctuating weakness and voluntary muscles that fatigue easily (EOMs affected first, generalized weakness, sxs worse at end of day).
What is revealed on physical exam in a patient with myasthenia gravis?
- asymmetric ocular palsy and ptosis (cannot maintain sustained up gaze or repetitive blinking)
- variable paresis
- normal sensation and reflexes
- muscle atrophy (late)
- ACh receptor antibodies (labs)
- EMG/NCV shows impaired transmission
What can a CT scan reveal in a patient with myasthenia gravis?
- thymoma (thymic medullary cells can synthesize anti-ACh receptor antibodies)
- may be revealed in 10-15% of patients
How is myasthenia gravis diagnosed and treated?
- dx: confirmed with edrophonium 2mg IV (short acting ACh-ase inhibitor) AKA "tensilon test" (transiently improves weakness)
- tx: anti cholinesterase drug (pyridostigmine 60mg QID), thymectomy (esp younger pt), corticosteroids (failure of other treatments), plasmapheresis (temp improvement in rapid deteriorating cases)
Presents as a systemic disorder causing bilateral muscle weakness of an unknown etiology, presents with characteristic manifestations of Gottran papules and a heliotrope rash. Diagnosed by elevated CK, may require muscle biopsy, EMG, and MRI.
Distinct pathologic processes that present very similarly except the skin manifestations, can affect pts of any age but is seen more commonly in black males in their 5th or 6th decades.
Between polymyositis and dermatomyositis which has a 1-4 increased risk of malignancy in adult patients?
May begin abruptly and usually presents as gradual and progressive muscle weakness, usually involves the proximal muscle groups of the upper and lower extremities including the neck. Leg weakness precedes the arms. There is no facial or ocular muscle weakness like in myasthenia gravis.
Patients with this disease may have pain but its not a usual presenting complaint. Presents with difficult in the initiation of swallowing because it affects the striated muscles and is until the "sticking" sensation associated with scleroderma due to its effects on the smooth muscle.
polymyositis and/or dermatomyositis
Muscle contractions and atrophy occur late in the advanced form of this disease, if pt is bed-bound must insure there is no respiratory weakness which can lead to CO2 retention to the point that mechanical ventilation is required.
polymyositis and/or dermatomyositis
Presents with a characteristic "shawl sign" dusky red rash affecting the face, neck, shoulders, upper chest and back. Mimics SLE. Also presents with periorbital edema and a purplish heliotrope suffusion over the eyelids and Gotton's sign.
Inhibits ACh esterase, the excess ACh continues to stimulate which causes organ overstimulation.
nerve agents (ie Soman)
What is used as a nerve agent pretreatment that was approved as a treatment for myasthenia gravis in 1995?
- pyridostigmine bromide
- Note: "hides" or protects a fraction of AChE (reserve force) which increases the amount of nerve agent a person can be exposed to and survive (does not interfere with military function)
Protects ACh esterase from degradation by irreversibly binding the nerve agent.
pralidoxime (aka 2PAM chloride)
Parasympathomimetic and reversible cholinesterase inhibitor. Since it is a quaternary amine it is poorly absorbed in the gut and does not cross the BBB except possible in stressful conditions.