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Flashcards in Chapter 18 Myofascial Pain Deck (56):

Myofascial pain disorders

heterogeneous group of
clinical entities that share features that originate from
soft tissue pain with resultant regional symptomatology


Examples of Myofascial Pain Disorders

episodic tension-type headache, myofascial pain syndrome, temporomandibular disorder, muscle cramps, and low back pain


Muscle pain is thought to occur by two main mechanisms:

peripheral and central


Peripheral factors of muscle pain

trauma, dysregulated deep-tissue microcirculation, and altered muscular metabolism and mitochondrial function. Mechanical, thermal, or chemical stimulation can lead to activation of intramuscular group III and group IV nociceptors, which in turn give rise to an inflammatory cascade mediated by immune cells, leading to further recruitment
of inflammatory cells and propagation of local inflammation and sensitization


Central factors of muscle pain

Pain transmission occurs along
Ad and C-fibers into the inner lamina of the spinal cord, where complex changes occur, leading to sensitization and
chronic pain. Continuous nociceptive input via these pathways can lead to central sensitization of higher-order neurons, --> enhanced sensitivity to painful stimuli via
excitatory glutamate and aspartate-related neurotransmitter release (hyperalgesia),reduced thresholds to nonpainful stimuli (allodynia), and increased receptive fields, causing referred pain


Supraspinal mechanisms contribute to chronic muscular pain states include

decreased cerebral activity, hippocampal suppression, and possibly impaired stress responses. Once central sensitization occurs, pain becomes autonomous from sensory input from the affected


The International Headache Society classifies tension-type
headaches (TTHs) as

infrequent episodic (,12 days/yr), frequent episodic (12 to fewer than 180 days/yr), and chronic (180 days/yr).


Pathophysiologic mechanisms responsible for TTH can be divided into

peripheral and central causes


Peripheral factors of tension-type headaches

Peripheral mechanisms are demonstrated by increased tenderness of pericranial myofascial tissue and increased electromyographic
and algometric pressure recordings


Central factors of tension-type headaches

Continuous nociceptive
input can lead to central sensitization, thereby converting episodic TTH into chronic headaches


Temporomandibular disorder (TMD)

is a broad term used to describe conditions arising in the jaw joint, muscles of mastication, and associated craniofacial structures. These conditions most commonly include pain, dysfunction, arthritis, and internal derangement


In patients with TMD Electromyographic recordings have demonstrated

altered muscular contraction,
as well as increased muscular tone


myofascial pain syndrome (MPS) characterizes by the

presence of loci of hypersensitivity within a tender, taut, palpable band of
muscle called a trigger point (TP)


trigger point

TPs are characterized by
referred pain on palpation and elicitation of a local twitch
response (LTR) with application of mechanical pressure


Trigger points can be classified into

active TPs or latent TPs.
Active TPs are described as pain in a motor locus
associated with spontaneous electrical activity, whereas
the more common latent TPs do not cause spontaneous
pain, but can be triggered by factors such as mechanical
stressors, dysfunctional postures, changes in weather, and either excessive immobility or the exaggerated use of muscles


What leads to the formation of a TP circuit?

It has been suggested that a positive feedback
cycle involving disproportionate acetylcholine release, sarcomere shortening, and increased concentrations of sensitizing substances leads to the formation of a TP circuit,
which upon connection with other spinal dorsal horn
neuronal pathways, activates latent TPs to become an
active TP


Spine structures functions,

protecting the spinal cord, maintaining posture and truncal stability, and acting as a steadying force for movement of the extremities.


Skeletal and ligamentous
structures serve as a

protective foundation from which attached muscles provide functional motor control, flexibility, and movement coordination


Weakness in the core muscles
(lumbo-pelvic-hip complex), unbalanced gait mechanics,
or dysfunctional muscular proprioception can
lead to

tears, strains, sprains, or spasm within the paraspinal musculature


True muscle cramps

painful involuntary skeletal
muscle contractions associated with electrical activity. EMG studies show fast rates of repetitive firing of motor units in affected muscles. True muscle cramps occur in the absence of fluid or electrolyte imbalance,


True muscle cramps are
more commonly found in patients with

well-developed muscles, in the third trimester of pregnancy, and in metabolic disorders such as cirrhosis and renal disease


causes of muscle cramps include

medications, lower motor neuron disease, hypothyroidism, and hereditary


Painful cramps can often be terminated by

stretching the cramped muscle.


Tricyclic antidepressants (TCAs)

amitriptyline, nortriptyline,
desipramine, and imipramine


Tricyclic antidepressants (TCAs) Mechanism of Action

provide analgesia
independent of their antidepressive effects by multiple mechanisms, which include norepinephrine and serotonin reuptake inhibition in inhibitory descending pathways. Other active mechanisms include blockade of peripheral neural sodium channels, muscarinic and nicotinic acetylcholine receptors, alpha adrenergic
receptors, NMDA receptors, substance P release, and to a
lesser extent, dopamine receptors


TCAs to be effective in
reducing the frequency and intensity of

tension-type headaches (TTHs) and facial pain/TMD.


Tricyclic antidepressants (TCAs)
use is limited secondary to

myriad side effects, which include dry mouth, constipation, fluid retention, weight gain, difficulty concentrating, and cardiotoxicity


TABLE 18–2

Tricyclic Antidepressants


Calcium Channel Antagonists
(Pregabalin and gabapentin)

an analog of GABA, exert their
analgesic effects by acting on the a2-d1 subunit of cellular
calcium channels and blocking neurotransmitter release.
Their binding to calcium channels results in suppression of abnormal neuronal discharges and an increased threshold for nerve activation


most common side effects of gabapentin and pregabalin

include dizziness, sedation, lightheadedness, somnolence,
and weight gain


first-line treatment for headache prophylaxis.



TABLE 18–3

Calcium Channel Antagonists


Gabapentin beneficial

in reducing spasticity in npatients with multiple sclerosis and spinal cord injury and for chronic
masticatory myalgia.


Usefullness of sodium valproate in Myofascial Pain

an anticonvulsant that acts via
a variety of mechanisms including the blockade of
T-type calcium and sodium channels, and facilitation of
GABA, have shown benefit in TTH and chronic daily


Skeletal muscle relaxants

cyclobenzaprine (Flexeril),
chlorzoxazone (Paraflex), carisoprodol (Soma), methocarbamol
(Robaxin, Robaxisal), tizanidine (Zanaflex), and
baclofen (Lioresal)


Skeletal muscle relaxants believed to exert their mechanism of action

primarily within the brain and in some cases spinal motor neurons


cyclobenzaprine (Flexeril)

Cyclobenzaprine, structurally related to first-generation tricyclic antidepressants, inhibits the reuptake of norepinephrine in the locus coeruleus and inhibits descending serotonergic pathways in the spinal cord. The latter effect may have an inhibitory effect on alpha motor neurons in the spinal cord, resulting in decreased firing and a reduction in mono- and polysynaptic spinal reflexes


tizanidine (Zanaflex)

Tizanidine acts as a weak agonist at alpha-2 adrenergic
receptors, and enhances presynaptic inhibition at spinal
motor neurons



a precursor of the sedative hypnotic meprobamate, is believed to produce muscle relaxation by blocking interneuronal activity in the descending reticular formation and spinal cord.



activates GABA-B receptors in the brain and reduces the release of excitatory neurotransmitters in both the brain and spinal cord. Baclofen also acts by inhibiting the release of substance
P in the spinal cord


Baclofen Indications

Strong—spasticity of spinal cord origin Moderate—cervical
dystonia, upper motor neuron
disease, stiff-person syndrome, acute back pain


Tizanidine indications

Moderate— spasticity, paravetebral muscle spasm


Carisoprodol Indications

Moderate—acute musculoskeletal pain, not for spasticity


Chlorzoxazone (Paraflex,
Parafon, Forte)

Exact mechanism unknown, likely inhibits polysynaptic
reflex pathways in spinal cord (central-acting)


Chlorzoxazone (Paraflex,
Parafon, Forte) indications

Moderate—acute musculoskeletal pain, back pain, acute lumbosacral muscle strain


Cyclobenzaprine( Flexeril) indications

Strong—cervical and lumbar spinal pain, muscle spasm
Moderate—TMD with myofascial pain


Skeletal Muscle Relaxants metabolism and excretion

Liver metabolism
and urine excretion;


Skeletal Muscle Relaxants
Adverse Side Effects

Dry mouth, drowsiness,
headache, diarrhea, constipation, dizziness, nausea,
confusion, lightheadedness,


Benzodiazepines Mechanism of Action

enhance presynaptic inhibition in the spinal cord by targeting inhibitory neurotransmitter receptors that are directly activated by GABA. Benzodiazepine receptor
binding facilitates GABA A receptor binding, increasing
the influx of negatively charged chloride ions across the cell membrane.


The increased membrane conductance leads to

hyperpolarization of Ia afferent terminals at neuronal These changes in membrane polarization lead to inhibition of normal neuronal transmission and reduced motor neuron output.synapse


Benzodiazepines Common side Effects

include dizziness, somnolence, confusion, memory loss, ataxia, sedation, and physical dependence with sustained use. Psychological effects include paradoxical anxiety, depression, paranoia,
and irritability



Diazepam (Valium),
Clonazepam (Klonopin), Alprazolam (Xanax), Midazolam (Versed)


Benzodiazepines Common
Adverse Side Effects

Drowsiness, dizziness, ataxia,
headache, nausea, somnolence, diarrhea, constipation, dry mouth,
fatigue, headache, tremor, dysuria, hypotension, tremor, sedation


Diazepam Indications

Strong—spasticity of spinal cord origin Moderate—chronic
orofacial muscle pain, tension-type headache Weak—TMD


Clonazepam Indications

Moderate—TMD with myofascial
pain, nocturnal muscle spasms


Alprazolam Indications


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