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Myofascial Pain Syndrome
Myofascial pain syndrome (previously known as myofascial pain and dysfunction syndrome [MFPDS]) can occur in patients with a normal temporomandibular joint. It is caused by tension, fatigue, or spasm in the masticatory muscles (medial or internal and lateral or external pterygoids, temporalis, and masseter). Symptoms include bruxism, pain and tenderness in and around the masticatory apparatus or referred to other locations in the head and neck, and, often, abnormalities of jaw mobility. Diagnosis is based on history and physical examination. Conservative treatment, including analgesics, muscle relaxation, habit modification, and bite splinting, usually is effective.
This syndrome is the most common disorder affecting the temporomandibular region. It is more common among women and has a bimodal age distribution in the early 20s and around menopause.
The muscle spasm causing the disorder usually is the result of nocturnal bruxism (clenching or grinding of the teeth—see Bruxism). Whether bruxism is caused by irregular tooth contacts, emotional stress, or sleep disorders is controversial. Bruxism usually has a multifactorial etiology. Myofascial pain syndrome is not limited to the muscles of mastication. It can occur anywhere in the body, most commonly involving muscles in the neck and back.
Symptoms include pain and tenderness of the masticatory muscles and often pain and limitation of jaw excursion. Both nocturnal bruxism and sleep-disordered breathing (such as obstructive sleep apnea and upper airway resistance syndrome—see Obstructive Sleep Apnea) can lead to headache that is more severe on awakening and gradually subsides during the day. Such pain must be distinguished from giant cell arteritis (see Giant Cell Arteritis). Daytime symptoms, including jaw muscle fatigue, jaw pain, and headaches, may worsen if bruxing continues throughout the day.
The jaw deviates when the mouth opens but usually not as suddenly or always at the same point of opening as it does with internal temporomandibular joint derangement (see Internal Temporomandibular Joint Derangement). Exerting gentle pressure, the examiner can open the patient’s mouth another 1 to 3 mm beyond unaided maximum opening.
A simple test may aid the diagnosis: two or three tongue blades are placed between the rear molars on each side, and the patient is asked to close the mouth gently. The distraction produced in the joint space may ease the symptoms. X-rays usually do not help except to rule out arthritis. If giant cell arteritis is suspected, ESR is measured.
Polysomnography should be done if sleep-disordered breathing is suspected.
A plastic splint or mouth guard from a dentist can keep teeth from contacting each other and prevent the damages caused by bruxism. Comfortable, heat-moldable splints are available from many sporting goods stores or drugstores; however, these types of splints should be used briefly and only as short-term diagnostic tools. Because teeth may move, mouth guards that are properly made and fitted by a dentist are recommended.
Low doses of a benzodiazepine at bedtime are often effective for acute exacerbations and temporary relief of symptoms; however, in patients with associated sleep disorders, such as sleep apnea, anxiolytics and muscle relaxants should be used with caution because they can aggravate these conditions. Mild analgesics, such as NSAIDs or acetaminophen, are indicated. Cyclobenzaprine may help muscle relaxation in some people. Because the condition is chronic, opioids should not be used, except perhaps briefly for acute exacerbations.
The patient must learn to stop clenching the jaw and grinding the teeth when awake. Hard-to-chew foods and chewing gum should be avoided. Physical therapy, biofeedback to encourage relaxation, and counseling help some patients. Physical modalities include transcutaneous electric nerve stimulation (TENS—see Electrical stimulation) and “spray and stretch,” in which the jaw is stretched open after the skin over the painful area has been chilled with ice or sprayed with a skin refrigerant, such as ethyl chloride. Botulinum toxin has recently been used successfully to relieve muscle spasm in myofascial pain syndrome. Most patients, even if untreated, stop having significant symptoms within 2 to 3 yr.
Myofascial pain syndrome is a more common cause of temporomandibular pain than temporomandibular joint derangement.
Tension, fatigue, and spasm of the masticatory muscles results from nocturnal bruxism.
Patients have pain and tenderness of the masticatory muscles, painful limitation of jaw excursion, and sometimes headache.
Bedtime use of splints or mouth guards and a benzodiazepine may help, along with nonopioid analgesics.
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