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Migraine Etiology Hypothesis
 

Sympathetically Maintained Spindular Dysfunction:

A Hypothesis for the Etiology of Chronic
Tension-type Headache
and Migraine

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 varying 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 ear 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 intensely than 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 to 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 skin 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 Tension-Migraine Cycle)

Preventing Migraine Pain without drugs or surgery

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.

"BOTOX" Injections

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 the structures surrounding their origins).

See: Botulinum toxin A for the treatment of headache disorders and pericranial pain syndromes, Nervenarzt 2001 Apr;72(4):261-74