James P. Boyd, DDS
Spindular dysfunction is a chronic tension of the intrafusal fibers of
the spindle organs of skeletal muscle, which are innervated by the sympathetic
nervous system. The chronic tension causes pain, tension and
fatigue and allows for acutely painful episodes.
Within every skeletal muscle which opposes gravity (postural and
masticatory), there exists specialized fibrous organs called spindle fibers.
Within each spindle fiber are intrafusal fibers, specialized muscle
cells which receive direct innervation from the sympathetic nervous
system. The sympathetic nervous system is responsible for reaction to threat
(i.e., "fight or flight response). It is now known that muscular"trigger points" are
actually dysfunctional spindle fibers. (žMyofascial Trigger
Points Show Spontaneous Needle EMG ActivityÓ Hubbard, Berkoff, SPINE, Vol.
18 #13, pp1803-07, 1993)
Normal sleep consists of several cycles per night. During
certain stages, particular muscles, notably the temporalis, contract with
degrees of frequency and intensity, unique to each individual. (The temporalis
muscle is considered the strongest muscle of the body, and is located
on the side of the skull, extending from the side of the eye to behind the
and is attached to a special projection of the lower jaw). When contracted,
the temporalis elevates, or closes, the mandible (lower jaw) until the teeth
come into contact. The temporalis is designed to clench and crush objects, primarily
utilizing the canine teeth, and secondarily the molars. Although all
humans clench their jaws occasionally during sleep, highly intense contraction
is considered a parafunctional event (an activity without specific purpose
that can be damaging is considered to be parafunctional).
The typical patient
with spindular dysfunction usually awakens with some degree of headpain,
and/or noticeable neck or scalp tension. In fact, it
is more rare for the typical sufferer to awaken pain free than in discomfort, although they rarely report this fact. These
patients typically clench their jaws during sleep on average 14 times more
non-sufferers do(žWaking and Sleeping
EMG Levels in Tension-Type Headache PatientsÓ JOP,vol.
11,#4,Ū97). Whereas to a "normal" person this degree of tension
might be considered a headache, to the patient with spindular
dysfunction, slight to moderate degrees of muscle discomfort and tension
are considered "normal" and unremarkable.
When the temporalis contracts with extreme intensity during the normal REM
sleep stage, the patient can be awakened from sleep with greater than usual
head pain, or awakens in the morning with a greater than their "normal" degree
of discomfort, which they then categorize as a headache.
As the frequency of the intense contractions increases, so does the
frequency and intensity of the symptoms, most obvious of which is chronic
tension-type headache. As the temporalis becomes chronically fatigued, the
spindle fibers within it become more sensitized, irritated and susceptible
intrafusal spasm. Since the spindle fibers are innervated by the sympathetic
nervous system (SNS), conditions which affect the SNS, such as stress, certain
foods, barometric pressure changes, bright light, hormonal
changes, etc., creates further tension within the spindle
fibers. The patient then assumes "stress gives them a headache, or makes
it worse". (žNeedle electromyographic evaluation of trigger point
response to a psychological stressorÓ McNulty, Hubbard, Gervitz,
Berkoff. Psychophysiology 31, 1994).
The typical migraine patient, upon being exposed to a "trigger" may sense
a tightening of the scalp or shoulders (the sympthetic innervation of the
intrafusal fibers causing their increased tension).
The result can be "spasm" of the intrafusal muscle fibers within the spindle
organ. This intrafusal fiber spasm can not be displayed on a traditional
pad EMG reading, but rather can only be recorded using a needle EMG, inserted
directly into the spindular organ itself. Unlike other typical
skeletal muscle spasm, intrafusal spindular fiber spasm can continue for
several hours and but similar to other skeletalmuscle spasm, can be tender,
sore or painful for several days after the acute episode. In addition
to being acutely painful, intrafusal spindle fiber spasm can be accompanied
by various sympathetic symptoms, such as nausea and sensitivity to light
(i.e., typical symptoms of "common migraine"). The
clinical presentation is that of migraineous pain,
which may originate from the temple (temporalis muscle), and/or behind the
eye (sphenomandibularis or zygomandibularis)
and/or the neck (trapezius), lasting potentially for hours and being
residually tender for days. (The Sympathetic
Treatment for spindular dysfunction is not directed at the actual event,
as most migraines medications are. Treatment is of a
preventive nature, aimed at suppressing the underlying chronically
intense muscle contractions, most notably, the temporalis, by using an anterior midline point stop
device that prevents canine and posterior occlusion in all excursive
positions. By suppressing the chronic intensity of nocturnal muscle
contraction, the environment in which the sensitized spindle resides in
improves greatly, thereby reducing or eliminating the resultant activity
produced by normal sympathetic input, i.e., migraine pain.
New clinical observations have shown that when accurately administered,
Botulism toxin (Botox) injected into certain scalp musculature eliminates or
reduces the frequency and/or intensity of migraine events. These
observations support the Spindular Dysfunction hypothesis. The toxin
paralyzes musculature for up to four months, and may entirely eliminate the
spindle altogether if injected directly into the intrafusal fibers.
However, the current protocol for Botox injections calls for the injections to
be placed throughout the forehead and base of the skull. Those
injections which are most laterally located on the forehead (into the anterior
temporalis) would have the greatest chance of targeting a dysfunctional
spindle. (Assuming the hypothesis is correct, injecting Botox into
the sphenomandibularis or zygomandibularis would be contraindicated due to
surrounding their origins).
toxin A for the treatment of headache disorders and pericranial pain
syndromes, Nervenarzt 2001 Apr;72(4):261-74