Pain Surgery Flashcards
A 55-year-old male with known ischemic heart disease develops a crushing chest pain which radiates into his neck and left arm. The phenomenon of referred pain is best explained by which one of the following mechanisms?
a. Pain transmission along a given afferent nerve is transferred to another afferent pathway due to ephaptic transmission
b. Lateral inhibition of secondary afferent
fibers by a single primary afferent
c. Convergence of primary afferent fibers from a specific part of the body onto second-order neurons that normally receive primary afferents from a different body part
d. Disruption of dorsal root ganglia
e. The blockade of substance P and glutamate in the dorsal horn
c. Convergence of primary afferent fibers from a specific part of the body onto second-order neurons that normally receive primary afferents from a different body part
Referred pain is a phenomenon in which pain
impulses, usually arising from primary visceral
afferent fibers from one part of the body, terminate on dorsal horn projection neurons that normally receive cutaneous afferents from a different part of the body (such as the arm). It is the convergence of these distinctly different inputs onto the same projection neurons that provides the basis for this phenomenon. However, other theories including central sensitization, thalamic convergence, and hyperexcitability have also been proposed. Pain signaling in the spinal cord dorsal horn is via glutamate (C fibers and A-delta fibers) and substance P (C fibers). The opioid peptides (enkephalin and dynorphin) are released by inhibitory interneurons
in the dorsal horns, medulla, and PAG and inhibit
transmission of pain impulses.
The descending pathway for central control of nociception is best described as involving which one of the following structures?
a. Anterior cingulate cortex fibers that synapse directly on dorsal horn neurons
b. Periaqueductal gray fibers that synapse nucleus raphe magnus neurons, which in turn synapse on dorsal horn neurons
c. Thalamic neurons that synapse upon red nucleus neurons, which in turn synapse upon dorsal horn cells
d. Hypothalamic fibers that synapse upon neurons of the nucleus solitarius that then synapse upon neurons of the dorsal horn
e. Thalamic fibers that synapse upon inhibitory interneurons in the dorsal horn
b. Periaqueductal gray fibers that synapse nucleus raphe magnus neurons, which in turn synapse on dorsal horn neurons
Periaqueductal gray stimulation activates
enkephalin-releasing neurons that project to the
nucleus raphe magnus, 5-HT release activates projections to inhibitory interneurons in Laminae II
(substantia gelatinosa). This results in release of
either enkephalin or dynorphin (endogenous opioid neurotransmitters), which bind to mu opioid
receptors on the axons of incoming nociceptive
C and A-delta fibers, inhibiting the release of substance P/glutamate from then and activation of
ascending pain pathways.
Which one of the following is not a potential site for ulnar nerve entrapment?
a. Arcade of Struthers
b. Heads of the flexor carpi ulnaris
c. Intermuscular septum
d. Osbourne’s fascia
e. Sublimis arch
e. Sublimis arch
Ulnar nerve at the elbow lies in the postcondylar
groove, then under the aponeurosis (Osbourne’s
fascia) then under the FCU itself. Initial benefit
following ulnar nerve transposition at the cubital
tunnel may be complicated by kinking at the
arcade of Struthers more proximally, which may
necessitate release at this level. Technique for
ulnar nerve decompression transposition is:
incision, identify, and protect/mobilize medial
antebrachial cutaneous nerve, identify ulnar nerve
proximal to Osbourne’s fascia, decompress distally
through leading edge of FCU (simple decompression); for transposition, extend decompression proximally by cutting intermuscular septum and
arcade of Struthers if present; assess position in full range of motion to ensure no subluxation. Recurrence of symptoms after decompression alone may suggest kinking/tethering at the intermuscular septum (or arcade of Struthers if not divided initially) requiring release
A 43-year-old woman is referred with a 2- year history of sharp, shooting pains radiating into the right side of her jaw. Each attack lasts for a few seconds but they seem to merge together so it can seem like several minutes of pain. After this she may be pain free for several hours. It is often triggered by eating/
drinking, brushing her teeth, touching her face, and talking. She denies any tearing, eye/eyelid changes or nasal congestion/rhinorrhea. There is no other past medical or family history. Neurological examination is
normal and MRI head was unremarkable.
Which one of the following is most appropriate first line therapy?
a. Baclofen
b. Carbamazepine
c. Gabapentin
d. Lamotrigine
e. Pimozide
b. Carbamazepine
The history is suggestive of trigeminal neuralgia
(tic douloureux). First line treatment is carbamazepine. Common side effects of CBZ: dizziness, vertigo, ataxia, diplopia, blood disorders, drowsiness, skin reactions. If CBZ not tolerated due to side effects could try oxcarbazepine (higher risk
of hyponatremia), or if allergic start gabapentin.
Other useful drugs include baclofen, phenytoin,
and lamotrigine
A 22-year-old female presents to her GP with a 3-month history of sharp, stabbing jaw pain and blurred vision on the right side. She is about to sit her examinations and is finding it difficult to study because of her symptoms.
Which one of the following would you wish to exclude as a priority?
a. Tolosa-Hunt syndrome
b. Multiple sclerosis
c. Intracranial tumor
d. Classical trigeminal neuralgia
e. Psychogenic pain syndrome
b. Multiple sclerosis
While the majority of cases of trigeminal neuralgia are due to vascular compression or idiopathic
(Classical), in a small proportion of cases it may be
the presenting feature of significant underlying
condition such as multiple sclerosis (brainstem
plaque causing ephaptic transmission), basilar
artery aneurysms, acoustic schwannomas, and
posterior fossa meningiomas, all of which may
cause injury to the fifth cranial nerve by compression. Red flag symptoms which should be
excluded include: sensory changes, deafness, difficulty achieving pain control, poor response to
carbamazepine, history of skin or oral malignancy
that could lead to perineural spread, symptoms in
ophthalmic distribution (more likely herpes zoster), under age of 40, symptoms suggestive of
optic neuritis, family history of MS. The
Tolosa-Hunt syndrome is a presumably inflammatory disorder that produces ophthalmoplegia
associated with headache and loss of sensation
over the forehead. Pupillary function is usually
spared, and the site of pathology is believed to
be in the superior orbital fissure or the cavernous
sinus. It is usually not associated with trigeminal
neuralgia.
Which one of the following statements
regarding surgical treatments for trigeminal neuralgia is LEAST accurate?
a. Microvascular decompression is a favored option for trigeminal neuralgia in MS
b. Radiofrequency thermocoagulation of
gasserian ganglion is most likely to cause
anesthesia dolorosa
c. Percutaneous destructive techniques
directed at the gasserian ganglion may
cause a trigemino-cardiac reflex
d. Balloon compression is usually performed under general anesthetic
e. Stereotactic radiosurgery of the trigeminal root only produces pain relief in a delayed fashion
a. Microvascular decompression is a favored option for trigeminal neuralgia in MS
Microvascular decompression is the gold standard
in good surgical candidates (i.e. classical trigeminal neuralgia, evidence of vascular compression
on MRI, short duration of disease, no previous surgery); pain relief is usually immediate and 60-
70% remaining pain free at 10-20 years. Indications include patients whose pain is no longer
controlled by drugs and whose quality of life has
markedly deteriorated, young patients, side
effects from antiepileptic drugs. The procedure
requires general anesthesia, and its adverse effects
include aseptic meningitis, ipsilateral hearing loss
(in less than 5%), CSF leak, low risk of sensory
loss, and death (0.4%). Stereotactic radiosurgery
targeting the trigeminal root does not require
general anesthesia, but its pain-relieving effects
are not immediate. Adverse effects include facial
numbness, paresthesias, and sensory complications. Percutaneous destructive neurosurgical techniques (radiofrequency thermocoagulation,
glycerol rhizolysis, or balloon compression) can
achieve immediate pain relief and can therefore
be considered for emergency management, but
50% of patients have recurrence at 5 years. Sedation or even GA is required, and it carries a risk of trigeminal-vagal reflex effects on the heart during lesioning and a very small risk of carotid injury or intracranial infection. Balloon compression
carries a risk of temporary trigeminal motor
dysfunction. Adverse effects include a facial
numbness, corneal numbness (risk of keratitis),
dysesthesias, and anesthesia dolorosa.
Gate control theory of pain is best described by which one of the following statements?
a. The thalamus gates pain perception in the cortex
b. The substantia gelatinosa gates nociceptive signals before they reach the thalamus
c. The dorsal root ganglion gates nociceptive signals before they reach the substantia gelatinosa
d. The nociceptive nerve endings gate pain signals by altering the ratio of C and
A-delta fibers activated
e. The dorsal columns gate nociceptive
signals by ephaptic transmission
b. The substantia gelatinosa gates nociceptive signals before they reach the thalamus
The 1965 gate control theory of pain by Melzack
and Wall proposed that there were three spinal
cord systems involved in pain transmission: the
substantia gelatinosa, dorsal column fibers, and
central transmission cells in the DH. The substantia gelatinosa functions as a gate that modulates signals before they reach the brain. Large
diameter fibers have inhibitory effects to “shut
the gate” whereas small diameter fibers carrying
noxious stimuli open the gate to pain transmission. In a simplistic view of this model, rubbing
of the injured area promotes proprioceptive (i.e.
large diameter) fiber input and reduces pain
perception. In the late 1990s, Melzack proposed
the neuromatrix theory, adding higher cortical
functions as key elements of pain transmission
and interpretation. Today, the experience of pain
is described as distributed in three dimensions:
cognitive, affective, and sensory. Frontal and
limbic areas are believed to subserve the
cognitive-evaluative component of pain. Limbic
cortex, cingulum, hypothalamus, thalamus, and various midbrain regions are thought to contribute to the motivational-affective component of
pain. Primary somatosensory cortex, thalamus,
spinothalamic tract, and local nerve endings are
involved in the sensory component of pain.
Which one of the following statements
regarding intrathecal drug delivery systems is LEAST accurate?
a. The intrathecal route results in higher subarachnoid drug concentrations, lower absolute drug doses, and avoidance of side effects associated with systemic dosing
b. Ziconotideis exclusivelyintrathecal analgesic which blocks a N-type calcium channel
c. Development of an catheter tip granuloma is particularly associated with morphine
d. Intrathecal baclofen has a potent analgesic effect
e. Indications for intrathecal drug delivery
do not include patient preference
a. The intrathecal route results in higher subarachnoid drug concentrations, lower absolute drug doses, and avoidance of side effects associated with systemic dosing
The continuous administration of analgesics via
the intrathecal route results in higher subarachnoid drug concentrations, lower absolute drug doses, and avoidance of side effects associated with systemic dosing (especially at high doses).
Additionally, concerns about opiate diversion
and analgesic compliance are reduced. Indications for intrathecal drug delivery for pain
control:
1. An established pain diagnosis has been
made classifying the symptoms as neuropathic, nociceptive, or mixed.
2. Pain is chronic or both chronic and progressive in nature owing to either a malignant or nonmalignant cause.
3. Pain should be present throughout nearly
the entire day.
4. Patients have failed to achieve analgesia
with conservative nonpharmacologic
modalities.
5. Patient is refractory or intolerant to orally
administered analgesics.
6. Corrective treatment addressing the pain
generator is not warranted.
7. Surgical contraindications to implanting
prosthetic hardware and accessing the
intrathecal space are absent (e.g. bacteremia, anticoagulation).
Although several agents are commonly used for
chronic intrathecal delivery, only three medications currently have FDA approval for long-term
intrathecal use: baclofen, morphine, and ziconotide. Ziconotide is exclusively intrathecal form of ω-conotoxin MVIIa that blocks a N-type
calcium channel on small myelinated and unmyelinated nociceptive afferents that are primarily localized in the superficial Rexed laminae (I and II). Intrathecal baclofen, a GABA-B agonist,
is primarily used to treat spasticity but may help
with pain associated with spasticity and dystonias.
Intrathecal delivery of medications can result
in several potential adverse events including
sedation, cognitive impairment, nausea, vomiting, pruritus, urinary retention, constipation,
hormonal dysfunction, and edema. The development of an inflammatory mass (granuloma) is particularly associated with morphine and increasingly hydromorphone, with high drug concentrations combined with low flow rate increase the risk of granuloma development. Presentation is with loss on pain control or newonset pain complaints or progressive myelopathy.
CT myelography or MRI with gadolinium contrast of the catheter tip region is necessary to confirm the diagnosis. In asymptomatic and
nonprogressive patients, weaning of intrathecal
medications and initiation of saline infusion can
produce spontaneous disintegration of the mass.
In patients with progressive or severe neurologic
compromise, urgent surgical decompression and
excision are recommended.
Which one of the following statements regarding motor cortex stimulation for pain is LEAST accurate?
a. Electrodes may be placed in the subdural or extradural space
b. Subdural placement of electrodes may be required to achievelowerlimb pain coverage
c. Risk of seizures is highest intraoperatively and during programming
d. Is appropriate for deafferentation pain
syndromes
e. Is not indicated in patients with multiple sclerosis related chronic pain syndromes due to high seizure risk
e. Is not indicated in patients with multiple sclerosis related chronic pain syndromes due to high seizure risk
Chronic stimulation of the precentral gyrus
below the threshold to produce a motor response
is able to alleviate certain types of deafferentation
pain and MCS has shown efficacy for a number of
deafferentation pain syndromes (e.g. trigeminal,
central post-stroke pain, anesthesia dolorosa,
post-herpetic neuralgia, multiple sclerosis, phantom limb pain, and spinal cord injury). The mechanism of action has been attributed to modulation of deafferentation-induced pathologic hyperactivity in thalamic relay nuclei and/or increased sensitivity of higher order pain pathway neurons.
Intraoperatively, the central sulcus is localized using SSEPs and a contact paddle electrode is placed in the epidural space overlying the facial or upper extremity region of the motor cortex. The electrode is then used for motor evoked potentials with electromyography to confirm motor activity. Iced saline is prepared for irrigation if a seizure is
induced. The minimum thresholds for motor activity and any seizure activity are noted. After confirmation, a paddle electrode is sutured to the dura over the precentral gyrus over the motor area that corresponds to the patient’s pain distribution. Subdural placement is associated with greater energy efficiency, but also an increased rate of complications, including subdural hematomas and a higher reported rate of seizures. However, opening of the dura may be necessary anyway for coverage of lower extremity pain, which requires placement of an electrode along the medial part of the hemisphere. MCS has an overall complication rate of about 5%: wound breakdown or infection (5.1%),
hardware breakage from trauma, and seizures
(12%). Stimulation of the motor cortex is known
to be associated with the potential to induce seizures, and most seizures observed during MCS
occur during programming sessions.
