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Trigeminal nerve (V)
Spinal nucleus
)
The Neurological Aspects of the Trigeminal Cranial Complex and Its Role in the TMJ Dysfunction…
163
The trigeminal nerve complex courses
within the middle cranial fossa before it
reaches the trigeminal (Gasserian) ganglion,
which lies posterolateral to the cavernous sinus
in an area called Meckel’s cave. Fibers from
the three nuclei intermingle at this point for
part of the mesencephalic, principal, and spinal
trigeminal nuclei, to send bers to the three
portions of the trigeminal nerve complex: ophthalmic (V1), maxillary (V2), and mandibular
(V3) nerves.
2.2 Trigeminal Nerve Branches (Fig.1)
Ophthalmic division branches: Frontal, lacrimal,
nasociliary, long ciliary nerves. Supplies sensory
afferents from the top of the head to the upper
eyelid, including the cornea
Fig. 1 Trigeminal nerve
branches
Maxillary division branches: Middle meningeal, nasopalatine, greater and lesser palatine,
zygomatic, and infraorbital. The maxillary division supplies sensory afferents from the lower
eyelid to the upper lip including sensation to the
gingiva and mucosa around the hard palate and
maxillary dentition
Mandibular division: Branches of the main
trunk (before splitting into anterior and posterior divisions) of the mandibular division
include meningeal, branch to medial pterygoid,
tensor tympani, and tensor veli palatini.
Branches of the anterior division include masseteric, lateral pterygoid, deep temporal, and
buccal. Branches of the posterior division
include auriculotemporal, lingual, and inferior
alveolar, which provides sensory afferents to
teeth as well as motor innervation to the mylohyoid and anterior belly of the digastric muscle
Motor nucleus
Main sensory
nucleus
Semilunar
trigeminal
ganglion
Ophthalmic
(V1 sensory
Maxillary
(V2 sensory
Mandibular
(V3 sensory
& motor)
164
A. B. Sims
3 Understanding theTrigeminal
Nerve andIts Connections
The trigeminal nerve (CN 5) is the largest and
most complex of 12 cranial nerves. Its vast size
and inuence are greatly appreciated when one
attempts to diagnose and treat patients suffering
from orofacial pain and temporomandibular joint
disorders. Without a thorough knowledge of the
trigeminal nerve, the efcacy of diagnostic and
therapeutic procedures will be very disappointing. CN 5 branches into three divisions: ophthalmic, maxillary, and mandibular divisions, each of
which supplies a distinct region or dermatome
that carries pain, touch, temperature, and proprioception from the face, eyes, teeth, jaws, and
mucosa of the nose, mouth, and anterior twothirds of the tongue. CN 5 carries about 140,000
sensory bers and about 8100 motor bers.
Sensory bers arise from the Gasserian ganglion (GG), but the sensory bers that determine
proprioception of the head come from jaw muscles and jaw position. These bers arise from the
mesencephalic nucleus in the brain stem. This is
an important factor to remember when evaluating
patients with cervical dystonia. Motor bers in
CN 5 originate from the trigeminal motor nucleus
and innervate the muscles of mastication.
The CN 5 sensory bers terminate in the trigeminal spinal nucleus or the principal/main
nucleus. Both send secondary neurons to the thalamus through the crossed ventral trigeminothalamic tract, which terminate in the ventral
posterior medial (VPM) nucleus of the thalamus
and are then sent through the thalamocortical
tract, which relays information from the facial
region to the cerebral cortex. The uncrossed dorsal trigeminothalamic bers also send signals to
the VPM.
The CN 5 is the only cranial nerve that has
direct rst-order neurons that input into the reticular formation, which is another important factor
in cases of movement disorders. The spinal
nucleus extends caudally and merges with the
substantia gelatinosa of the spinal cord and has
three divisions: spinal trigeminal oralis, trigeminal spinal interpolaris, and trigeminal spinal caudalis. The trigeminal spinal nucleus is also
connected to the motor nucleus along with the
ocular, trigeminal, facial, vestibular, glossopharyngeal, vagal, and hypoglossal nerves in the
brain stem. There are also afferent bers to the
superior colliculus, cerebellar cortex, and deep
cerebellar nuclei. Nerve bers also connect the
trigeminal with cervical nerve root bers C1, C2,
and C3.
The reticular formation (RF) is the central
core of the brain stem tegmentum. The RF
consists of multipolar neurons with long ascending and descending axons which interact with
collateral interneuron branches synaptically and
form complex loops and/or circuits. It has no distinct architectural boundaries and forms the central gray matter of the midbrain, pons, and
medulla. The brain stem’s RF has a modulatory
effect on the spinal cord, brain stem’s cranial
nerves, cerebrum, and cerebellar cortex. The
ascending reticular pathways encompass the
reticular activating system which regulates the
sleep-wake cycle and moderates awareness. The
descending reticular pathways moderate motor
activities within the spinal cord at all levels.
The trigeminal nerve is the only cranial nerve
with monosynaptic projections into the reticular
formation. Other behaviors of the RF include
control of body posture, orientation of the head
and body towards external stimuli, control of eye
movements, rhythm generator for diaphragm and
respiratory muscles, blood pressure control and
blood volume among organs, heart rate, reexes,
and inuence on our mental states. The RF neurons integrate nuclei from the CN 5, facial, glossopharyngeal, and oculomotor that ascend and
descend within the brain stem. The RF also connects to the thalamus, hypothalamus, cerebrum,
and cerebellum via ascending reticular neurons.
The trigeminoreticulothalamic pathway conveys
pain and temperature. There are also interneuronal connections within the RF.
The CN 5 system has many branches that supply innervation to different areas of the head and
facial structures (Fig.2). One of the structures of
the face that gets utilized the most is the temporomandibular joint (TMJ). It is constantly used for
mastication, speaking, facial expression, swallowing, and airway maintenance. The TMJ is the
Lesser
Au
The Neurological Aspects of the Trigeminal Cranial Complex and Its Role in the TMJ Dysfunction…
Fig. 2 https://www.
muhadharaty.com/
lecture/19573/%D8%
AF%D9%83%D8%AA%
D9%88%D8%B1%D8%B3%D8%B9%D8%
AF/mandibular- nerve- pptx
Facial nerve
riculotemporal
nerve
petrosal
nerve
V2 sensory
root
V3 motor
root
165
Otic
ganglion
articulation between the mandible and the cranium. This articulation is a bilateral movable fulcrum. The major skeletal components of the TMJ
are the mandible and the temporal bone. The
sphenoid and hyoid bones play a secondary supporting role in the articulation. There are two cartilaginous components, the articular cartilage and
the brocartilage disc, which separate the temporal bone from the mandible creating upper and
lower compartments within the TMJ, which contain the stylomandibular, sphenomandibular, and
Pinto’s (malleomandibular) ligaments. The muscles that support the TMJ are the temporalis, the
masseter, the medial and lateral pterygoids, the
suprahyoids, the infrahyoids, the geniohyoid, the
digastric, the mylohyoid, the styloid, and a multitude of cervical muscles. The main innervation of
the TMJ is the mandibular branch (V3) of CN 5
via the auriculotemporal (AT) nerve.
The AT nerve arises typically by two roots,
which encircle the middle meningeal artery. The
nerve passes posteriorly deep to the lateral pterygoid and is sandwiched between the sphenomandibular ligament and the neck of the mandible
condyle. The AT nerve is intimately associated
with the parotid gland, and it then travels poste-
rior to the TMJ.The terminal branches of the AT
nerve go on to innervate the scalp around the
temple. In addition, the AT nerve anastomoses
with the facial nerve and the otic ganglion. The
two branches which communicate with the facial
nerve do so at the posterior aspect of the masseter
muscle.
The AT nerve has ve main branches. These
are the anterior auricular, articular, parotid,
supercial temporal, and branches to the external
auditory meatus. The anterior auricular branches
innervate the skin overlying the tragus as well as
the adjacent part of the helix. The articular
branches go on to innervate the posterior aspect
of the TMJ, to which it is closely related. The
parotid branches provide secretomotor innervation. Another component of this originates from
cranial nerve IX, the glossopharyngeal nerve, via
its tympanic branch and transverses to the otic
ganglion. The bers then pass with the AT nerve
and innervate the parotid gland. The supercial
temporal branches run with the supercial temporal artery. These branches innervate the tissue
over the temple and coalesce with the facial
nerves. The branches to the external auditory
meatus run between the cartilaginous and bony
166
A. B. Sims
Fig. 3 Schematic of an integrated network model including the trigeminal sensory nuclear complex (TSNC) neurons in the facial motor neurons (FMNs), trigeminal
motor neurons (TMNs), and upper cervical motor neurons. Projections to muscles most affected by dystonia are
indicated by the hatched arrows. Ascending projections
from the TSNC to the motor cortex via the thalamus, and
to the superior colliculus (SC) and the reticular nuclei,
also modulate excitability via descending tracts to motor
nuclei (blue). Excitatory inputs to the cerebellum and
inhibitory inputs via the inferior olive (IO; green) contribute to cortical and bulbar descending modulation of motor
ear canals and innervate the skin of the meatus
and also provide innervation to the tympanic
membrane (Fig.3).
4 Temporomandibular Joint (TMJ)
The temporomandibular joint (TMJ) is a diarthrosis, better dened as a ginglymoarthrodial
joint, which means a composite anatomical joint
of which one element has an axial or hinge
motion and the other a simple gliding motion.
The TMJ is composed of a synovial cavity, artic-
neurons innervating muscles affected by dystonia via cerebellar outputs to the red nucleus, reticular nuclei, basal
ganglia, and motor cortex via the thalamus. TSNC projections to the basal ganglia (yellow) modulate excitability of
descending projections to motor neurons by outputs to the
motor cortex (via the thalamus), superior colliculus, red
nucleus, and pedunculopontine nucleus (PPN).
Connections from pedunculopontine nucleus to spinal
cord are not shown in the simplied gure. [From
Bradnam L, Barry C.The role of the trigeminal sensory
nuclear complex in the pathophysiology of craniocervical
dystonia. J Neurosci. 2013 Nov 20;33(47):18358–67]
ular cartilage, and a capsule that covers the same
joint. The TMJ through its complex movements,
in different orthogonal planes and multiple rotation axes, works in synergy with all the structures
just listed. The TMJ must also work in coordination with the contralateral TMJ to coordinate tandem dynamic function with the head’s cranial
system, the neck musculature, the dental occlusion, the facial structures, and the nervous system
components within these structures.
There may be developments within the TMJ
system that may cause various disorders to occur.
These include growth, disease, arthritis, dysfunc-
The Neurological Aspects of the Trigeminal Cranial Complex and Its Role in the TMJ Dysfunction…
167
tion, and microtraumas or macrotrauma disorders.
Whenever there is a mal-relation between any of
these structures, a dysfunction may result within
the trigeminal afferent nervous system, which in
turn may cause the various central nervous systems, as discussed above, to be a factor that produces movement disorders.
4.1 Growth Disorders
Disorders of the facial structure and the TMJ are
due to several factors in their development. There
may be maxillary or mandibular overgrowth or
undergrowth, which can be a result of (1) airway
obstruction (poor swallowing habits), (2) parafunctional habits (bruxism, thumb/nger sucking),
(3) allergies (enlarged tonsils and/or adenoids), (4)
misaligned teeth (maxillary and mandibular teeth
do not occlude properly), and (5) family genetics
(familial growth patterns). Growth disorders such
as condylar hypoplasia or hyperplasia and neoplasms may need to be treated to harmonize the
facial structures in certain cases.
4.2 Arthritic Disease
Osteoarthritis (OA) is a disease that causes degeneration of the articular cartilage sometimes known
as degenerative joint disease of the condyle or the
articular eminence of the temporal bone. The cartilage within the joint begins to break down, and
the underlying bone changes. These changes
develop slowly and worsen over time. OA can
cause pain, stiffness, and swelling. Crepitus sensation of sound could be the result of disk degeneration or perforation, causing bone- on- bone contact
and erosion. Joint involvement is usually bilateral.
X-rays or cone beam CT may show degeneration
and/or attening of the condylar head.
4.3 Infectious Arthritis
Infection of the TMJ may result from an infection of blood-borne organisms. The joint
becomes inamed, and jaw movement is pain-
ful with decreased motion. X-rays are usually
negative early but may show bony degeneration in the later stages. Diagnosis should be
made early to prevent permanent joint
dysfunction.
4.4 Traumatic Arthritis
Acute injury (e.g., from difcult tooth extraction
or endotracheal intubation) is a consistent factor
that leads to arthritis of the TMJ. Pain, tenderness, and limitation of mandibular motion may
occur. Diagnostic history is the most important
element when X-ray results are negative or when
intra-articular edema or hemorrhagic widening of
the joint space is not present.
4.5 Rheumatoid Arthritis
Rheumatoid arthritis of the TMJ affects approximately 17% of adults and children. Limited
movement, pain, and swelling are the most common symptoms. Children display destruction of
the condyle which results in mandibular growth
disturbance and facial deformity, and ankylosis
may develop in which surgery for correction may
be necessary. X-rays of the TMJ are usually negative in early stages but often show late-stage
bone destruction, which may result in an anterior
open-bite malocclusion.
5 Dysfunction oftheTMJ
Research from the National Institutes of Health
in the United States purports that the prevalence
of temporomandibular joint dysfunction in the
current population is between 5 and 12%. TMJ
disorders are at least twice as prevalent in
women as men. The most frequent sign for this
dysfunction was a clicking sound in the TMJ,
which was reported in all age groups. Clicking
is the main distinctive sign of an “internal
derangement” or dysfunction of the
TMJ.Internal derangements of the TMJ can be
classied as:
168
A. B. Sims
1. Reciprocal clicking (dislocation with
reduction)
2. Intermittent clicking (dislocation with
reduction)
3. Closed lock (dislocation without reduction)
Internal derangements of the TMJ involve a temporary, semipermanent, or permanent destruction of
the normal relationship between the condyle, the
disc, and the articular eminence. The etiologies of
internal derangements are categorized as:
1. Acute macrotrauma possibly due to mandibu-
lar whiplash, a blow to the mandible, and/or
mandibular hyperextension (intubation)
2. Chronic microtraumas possibly due to brux-
ism and/or clenching, excessive joint overload
causing joint degeneration, and loss of posterior teeth which support the dental arches
3. Occlusal interferences, possibly causing
stressful bruxism and/or malocclusion
4. Development from mandibular hyper- or
hypoplasia with/without facial asymmetry
Whenever clinicians speak about dysfunction
of the TMJ and neurological aspects of the joint,
the main complaint is pain. There are many levels
of pain from light touch or slight irritation to
severe pain. Pain during mechanical stimulation
of the joint and spontaneous pain are major
symptoms of degeneration. An important neuronal process of mechanical hypersensitivity of the
joint is the sensitization of thin myelinated
A-delta bers and nonmyelinated C bers innervating the joint.
Pain is a human primate instinct and can be
dened as a distressing sensation, as well as an
emotional experience that is linked to actual or
potential tissue damage, with the sole purpose of
notifying the body’s defense mechanism to react
towards a stimulus in order to avoid further tissue
damage. Both nociceptors remain silent during
homeostasis in the absence of pain and are activated when there is a potential of noxious stimulus. Both these nociceptors have specialized free
nerve endings that are widely located in the skin,
muscle, joint capsule, bone, and some major
internal organs.
There are three major roles for the receptors in
the primary afferent neurons which are excitatory, sensitizing, and inhibitory responses. Once
these receptors are being stimulated and have
reached the pain threshold, the resulting impulses
are propagated along the afferent bers towards
the dorsal horn (peripheral nervous system) and
medulla (cranial). The auriculotemporal nerve, a
branch of the mandibular portion (V3) of the trigeminal nerve, was found to innervate the lateral
capsule of the TMJ.In 75% of the specimens, the
masseteric nerve, a branch of the maxillary portion (V2) of the trigeminal nerve, was also found
to innervate the anteromedial capsule of the TMJ.
5.1 Relationship toCervical Spine
The cervical spine plays a major role in the stabilization of the cranium and balancing of the masticatory musculature through specic joint
articulations and muscle attachments. Postural
abnormalities that affect the static relationship
between the head and neck can possibly lead to
temporomandibular dysfunction, and the reverse
is also true. Abnormal posture can result in compression of the suboccipital muscles, produce
referred pain to the TMJ area, and alter the normal resting position of the mandible through
compression forces of the musculature or compression of the nerves that supply the TMJ.Some
patients progress to the point of chronic pain and
are given a diagnosis of myofascial pain dysfunction syndrome (MFPDS).
The upper quadrant of the cervical spine consists of the suboccipital muscles, cervical spine
from C1 to C7, mandible, TMJ, cranium, maxillary and mandibular dentition, cervicothoracic
area, rst and second ribs, hyoid bone, sternum,
clavicle, shoulder girdle, sternocleidomastoid
muscle (SCM), and upper extremities. A dysfunction from one area of the quadrant or any
combination can elicit pain and/or a dysfunction
of other portions of the quadrant. The quadrant
acts as one unit to convey proper movement and
position of the rest. These muscles and bones are
innervated by cranial nerves C1–C4, facial, glossopharyngeal (IX), vagus (X), and trigeminal
The Neurological Aspects of the Trigeminal Cranial Complex and Its Role in the TMJ Dysfunction…
169
nerve (V). The interface between these nerves is
called the trigeminocervical complex, and sometimes differentiation between them is difcult to
discern.
The subnucleus caudalis of the trigeminal
nerve contains a portion of the substantia gelatinosa that is continuous with the dorsal horn of the
spinal cord. The spinal accessory nerve (XI) connects with the superior ganglion of the vagus,
anastomoses with neurons from C2 to C4 spinal
segments, and is an efferent portion of the pharyngeal plexus and vagus. A large portion of the
spinal accessory nerve crosses the midline, which
may cause referred pain or dysfunction from the
SCM.The inferior ganglion of the vagus receives
transmission from the hypoglossal nerve, which
also joins with the pharyngeal plexus and spinal
C1 nerves to form the ansa cervicalis. Therefore,
the trigeminocervical complex involves cranial
nerves 5, 7, 9, 10, 11, and 12 and spinal nerves
C1–C4 and must include the reticular formation.
5.2 Trigeminal Nerve andPosture
Posture refers to the position of the human body
when standing and its orientation accounting for
its effects from gravity (Fig.4). Through mechanisms of feedback and feed-forward, postural
adjustments play a critical role in orthostatic and
dynamic postural control. Afferent inputs that
control posture are exteroceptive (skin sensitiveness of feet), proprioceptive (especially from the
cervical, hip, ankle, and knee joints), vestibular
(utriculus, sacculus, and semicircular canals),
and visual (movement of the surrounding
environment).
The neurons for proprioception are exceptional. Their unipolar cell bodies constitute the
mesencephalic trigeminal nucleus, which is lateral to the periaqueductal gray matter and extends
rostrally to the level of the superior colliculus.
The axons of these neurons form the mesence-
phalic trigeminal tract and are then distributed
with the maxillary and mandibular divisions of
V. They go to muscle spindles, receptors in the
temporomandibular joint, and pressure receptors
around the roots of the teeth. This pressure sense
is related to proprioception; reex connections to
the motor trigeminal nucleus regulate biting and
chewing.
The stomatognathic system (SS) also plays an
important role in postural control. The SS is a
functional unit characterized by several structures: skeletal components (maxilla and mandible), dental arches, soft tissues (salivary glands,
nervous and vascular supplies), and TMJ and
masticatory muscles (MM). When the occlusal
relationship is lost either unilaterally or bilaterally, the body posture may take on an unusual
position, causing neck or shoulder pain. In
patients with TMJ disc dysfunction, there can be
hyperlordosis of the thoracic spine (rectication)
and head (deviation to the right or left).
The muscle combinations of the SS are a part
of the cervical muscular chain, and the musculoskeletal system is composed of several muscular
chain groups. They are all integrated together.
Any disorder of one body segment will result in a
reorganization or adaptation of other muscular
segmental group [3]. For example, studies have
shown that the simulation of a atfoot increased
muscular stimulation of the temporal and masseter musculature.
The cerebellum regulates the cognitive and
automatic processes of posture-gait control by
acting on the cerebral cortex via the thalamocortical projection and brain stem, respectively. The
basal ganglia may also contribute to the modulation of each process through projections to the
cerebral cortex and brain stem. It is also generally
agreed that the reticulospinal tract (RST) contributes to regulation of the level of muscle tone.
There may exist functional organization in the
reticular formation in relation to the control of
postural muscle tone. Muscle tone related to RST
participates in the execution of locomotion so
that locomotor rhythm and muscle tone can be
simultaneously regulated by the reticulospinal
system during locomotion.
The trigeminal spinal nucleus has extensive
projections to motor neurons in the spinal cord,
the brain stem’s reticular formation, the cerebellum, and the basal ganglia, and via the thalamus to
the motor cortex. Aberrant cerebellar circuitry is
linked to many forms of spinocerebellar ataxias
170
P
e
To head area
of primary
somesthetic
Ventral posterior
medial nucleus
of thalamus
Tr igeminal
lemniscus
Motor trigeminal
nucleus
ontine trigeminal
nucleus
Spinal trigeminal
nucleus
cortex
Tr igeminal
ganglion
A. B. Sims
Mesencephalic
trigeminal nucleus
Proprioception; pressur
from sockets of teeth
To muscles
Touch
Pain and
temperature
Fig. 4 The pathway of trigeminal pain. The spinal trigeminal tract connects the pons to the cervicomedullary
junction, where trigeminal pain impulses are sent to the
including impaired balance and motor coordination. In order to achieve smooth and balanced
muscle movement, the cerebellum receives input
from the sensory systems which includes the trigeminal nerves, the spinal cord, the reticular formation, and other parts of the brain. The trigeminal
nerve is the only cranial nerve that carries primary
deeper second-order nucleus caudalis. Signals to the contralateral thalamus are sent by the ventral trigeminothalamic tract
ment in these disorders is in a conscious patient.
Some movement disorders are known to be associated with hereditary changes, environmental exposures, and pathological changes. Some have a
well-known origin (i.e., Parkinson’s disease)
where others are not totally clear and thought to be
idiopathic (i.e., Tourette syndrome, tremor).
afferent neurons to the reticular formation, thus
having primary inuence on the reticulospinal
system through which the nervous system can
facilitate or inhibit motor movement and posture.
6.1 Hyperkinetic Movement
Disorders
Hyperkinetic movements are unwanted or excess
6 Movement Disorders
movements that are frequently seen in children
with neurologic disorders. Dystonia is a move-
Movement disorders can be dened as neurological syndromes in which there is either an excess of
movement (hyperkinesia) or a paucity of voluntary
and automatic movements, unrelated to weakness
or spasticity (hypokinesia). The abnormal move-
ment disorder in which involuntary sustained or
intermittent muscle contractions cause twisting
and repetitive movements, abnormal postures, or
both. Chorea is an ongoing random-appearing
sequence of one or more discrete involuntary
The Neurological Aspects of the Trigeminal Cranial Complex and Its Role in the TMJ Dysfunction…
171
movements or movement fragments. Athetosis is
a slow, continuous, involuntary writhing movement that prevents maintenance of a stable posture. Myoclonus is a sequence of repeated, often
nonrhythmic, brief shock-like jerks due to sudden
involuntary contraction or relaxation of one or
more muscles. The previous three movement disorders will not be addressed in this chapter.
Tremor is a rhythmic back-and-forth or oscillating involuntary movement about a joint axis. Tics
are repeated, individually recognizable, intermittent movements or movement fragments that are
almost always briey suppressible and are usually
associated with awareness of an urge to perform
the movement. Stereotypes are repetitive, simple
movements that can be voluntarily suppressed.
6.2 Hypokinetic Movement Disorders
Hypokinetic movement is the term used concerning slow or reduced movement regarding speed
and amplitude. Hypokinetic movement disorders
are often referred to as Parkinsonism because
they display clinical features of idiopathic
Parkinson’s disease (IPD) such as rigidity and/or
bradykinesia. Tremor and postural and gait instability are usual signs and symptoms. Parkinson’s
disease is under the umbrella of Parkinsonism.
Though the assemblage of symptoms for
Parkinson’s disease may include the former,
Parkinsonism may have other causes or origins.
7 Dystonia
Dystonia is an abnormal movement depicted by
sustained muscle contractions that frequently
produce involuntary twisting and repetitive
movements, abnormal postures, and/or any combination of these. Dystonia often involves various
body parts and according to the site determines
its classication. Classications are (1) focal:
usually involving a specic part; (2) segmental:
usually involving two or more contiguous body
parts; (3) multifocal: involving two or more body
parts that are not contiguous; (4) hemidystonia:
usually involving one half of the body; and (5)
generalized: usually involving the legs.
The disease course can be either static or progressive. The variability can have four different
patterns: (1) persistent: dystonia that persists to
approximately the same extent throughout the day;
(2) action specic: dystonia that occurs only during a particular activity or task; (3) diurnal uctuations: dystonia uctuates during the day, with
recognizable circadian variations in occurrence
and severity; and (4) paroxysmal: sudden self-limited episodes of dystonia usually induced by a trigger with return to preexisting neurological state.
The etiology of the disorder is thought to be
either (A) inherited, (B) acquired, or (C) idiopathic. The classication “primary dystonia”
indicates that there are no obvious neurological
degenerative changes or other structural defects.
They are either generalized or focal dystonia.
Dystonia has been associated with injury to the
basal ganglia, in particular the putamen and globus pallidus. However, recent research has demonstrated that no basal ganglia injury can be
identied, and recent evidence from both human
disease and animal models suggests that other
brain areas including cerebellum, brain stem, or
sensory cortex can be causes of dystonia.
7.1 Types ofDystonia
7.1.1 Cervical Dystonia
This is the most common form of primary focal
dystonia. It was once thought to have a psychogenic etiology. It usually begins between 30 and
50years of age and is more prominent in women
than men. Cervical dystonia is also known as
spasmodic torticollis and is a rare neurological
disorder that is believed to originate in the brain.
It is classied by involuntary muscle contractions in the neck that cause abnormal movements
and postures of the head and neck. These contractions may be unremitting or unabating; they
may also present as spasms that can resemble
tremor. The severity of cervical dystonia can
vary, but the disorder can cause signicant pain
and discomfort as well as difculties due to
abnormal postures.
172
A. B. Sims
Abnormal head postures encompass combinations of rotation (torticollis), extended head posture (retrocollis), forward exion (anterocollis),
and lateral tilt (laterocollis). Dystonia tends to
increase with fatigue, stress, and upset emotions
and is relieved with rest and sleep. One factor that
is interesting about dystonia is the temporary relief
a patient may get utilizing what is called a “sensory trick” or geste antagoniste. It was recently
renamed as “alleviating maneuver” by Patel etal.
The phenomenology is varied, and the exact
mechanism remains elusive. These tricks are usually tactile or from proprioceptive stimuli. For
cervical dystonia, the patient places their hand on
the chin or side of the face to relieve their symptoms. There is no single strategy for the treatment
of cervical dystonia. Most therapies are to relieve
symptoms of pain, disturbed postures, functions,
and/or spasms.
The three treatment options, which may be
used alone or combined, are (1) botulinum toxin
injections, which is the rst-choice treatment; (2)
oral medications, of which there is no current
FDA-approved medication, levodopa, baclofen,
and clonazepam; and (3) deep brain stimulation
surgery, which involves placement of electrodes
into the brain and to reset brain wave patterns. The
precise mechanism action for this is not clear.
Currently, a combination of DBS and botulinum
toxin injections is being utilized as treatment.
Blepharospasm is an abnormal contraction of
the eyelid muscles. It often refers to benign
essential blepharospasm (BEB), which is a bilateral condition and a form of focal dystonia leading to episodic closure of the eyelids. Symptoms
usually begin as mild and infrequent spasms that
progress over time to forceful and frequent contractions of the eyelids, in advanced cases causing functional blindness from inability to
temporarily open the eyes. The rst-line treatment for BEB is periodic injection of botulinum
toxin into the eyelid muscles. Meige’s syndrome
is a combination of eyes, jaw, and facial
dystonias.
Blepharospasm is an increased frequency of
blinking and/or forceful eyelid closure with difculty or inability in opening the eyes. Eyelid
closure may last for seconds to minutes. This
may result in difculty in reading, driving, or
watching television. These symptoms can
become severe enough to cause the patient to
have a “functional blindness.” Patients often
complain of sensitivity to bright light (photophobia). There are alleviating maneuvers such as
humming, singing, talking, and even chewing
gum. Treatment for blepharospasm is the same as
with other dystonias: oral medications, botulism
toxin injections into the upper eyelids, and orbicularis oculi myectomy surgery (removing part
of the eyelid muscle) (Fig.5).
7.1.2 Oromandibular Dystonia (OMD)
Patients experience spasms of the face, mouth,
tongue, and lower jaw. The masticatory muscles
upon opening or closing produce lateral torsion,
protrusion, spasms, and/or a combination of these
symptoms of the jaw. Dystonic spasms may be seen
as nasal contractions, facial grimacing, lip pursing
or sucking, bruxism, tongue dyskinesia, mouth corner retractions, and platysma spasms. Breathing difculties have also been reported. Dysfunctions
include impaired mastication, dysphagia, speech
alterations (dysarthria and dysphonia), unconscious
opening and closing of the mandible, pulling and
twisting of the mandible forward or laterally, and
temporomandibular disorders (TMDs). Lingual
dystonia is produced by lateral deviation of the
tongue and/or protrusion of the tongue.
Trismus, bruxism, and forceful involuntary
jaw closure or temporomandibular joint (TMJ)
dislocation can lead to trauma and damage of the
oral cavity structures, dental restorations, dentures, excessive dental wear, dental fractures, and
trauma of the lips, gums, and tongue, while jawopening dystonia may be associated with TMJ
overload. Alleviating maneuvers of OMD are
touching the chin, talking, chewing gum, and biting on a toothpick. Some common predisposing
factors associated with OMD movement disorder
include tooth loss, loss of vertical dimension, illtting full dentures, an edentulous state, trauma,
and long dental procedures. Treatment of choice
for OMD is botulism toxin. OMD rarely improves
with medication, whereas there are no surgical
options. Even botulism toxin has its difculties
because it can be complicated by postinjection
swallowing difculties, which could render the
procedure life-threatening.