How to Diagnose Masticatory Muscle Disorders

Man in Pain Sitting on a Couch Holding His Head, Possibly Suffering from a Masticatory Muscle Disorder

Localized Myalgia

Localized myalgia is a term used to describe a dull aching continuous which the patient localizes to muscles in the masticatory system (usually the masseter and temporalis) or cervical muscles (SCM and trapezius).  If the myalgia is in masticatory muscles, the International Classification Disease (ICD-10) code is M79.11, and if is in cervical muscles, will be M79.12.

Related Reading: How to Measure Orofacial Pain With a Muscle Tenderness Exam

The pain is usually variable pain and is confirmed by palpation of the involved muscle.  The important issue when diagnosing localized myalgia is to identify the cause for the muscle pain, which is not done via the examination, but by a careful medical and habit history.  This diagnosis is used when the pain and palpation findings do not qualify as a myofascial pain (see below).  Palpation is performed using a 2-second sustained pressure (2 kg of force).

Clinical History and Examination Evidence Needed to Diagnose Localized Myalgia

  1. The patient has a complaint of pain which the patient localizes to a muscle (e.g. jaw or neck)
  2. There is moderate or severe tenderness on the jaw and/or cervical muscle palpation
  3. The pain is rated by patient on a none, mild, moderate, severe rating scale

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Myofascial Pain (ICD-10 M79.18)

In a muscle that the patient reports pain and you can identify moderate to severe tenderness, you should next examine the muscle for taut bands.  If you find one or two taut bands, and within the band you can identify painful trigger points that when compressed causes referred pain, this is called a myofascial trigger point and the diagnosis used is Myofascial Pain (MFP).  This problem can affect multiple muscles in the body and when present, often includes both the masticatory and/or cervical muscles.

Related Reading: Oral Motor Disorders: Hemi-Facial Spasms

Clinical History and Examination Evidence Needed to Diagnose Myofacial Pain

  1. A subjective complaint of pain, which the patient localizes to the jaw or neck muscles
  2. Palpable taut muscle bands within the muscle when you move the overlying skin back and forth over the muscle with your fingers as you apply pressure (approximately 1 kg)
  3. Palpable moderate to severely tender trigger points are within the taut band
  4. Referred pain sensations on sustained palpation of this point (up to 3 seconds)

Related Reading: Closed Lock Mobilization: TMJ Exercises & Stretches

Fibromyalgia (ICD-10 M79.7)

If you have multiple areas of widespread myofacial pain (MFP), the next consideration is, does this quality as fibromyalgia.

In 2010, the American College of Rheumatology (ACR) put forth updated criteria for the diagnosis of fibromyalgia.  The criteria are based on the wide spread pain (WPI) score and the symptom severity (SS) score plus two other criteria.

To determine the WPI you count the number of sites (from 19 specific anatomic sites) where the patient has pain and symptoms over the past week (WPI score is the total of positive sites).  To determine the SS score you rate four symptoms on scale of 0 to 3.  The four symptoms are fatigue, waking unrefreshed, cognitive symptoms, and general overall somatic pain symptoms.

The rating scale for items 1-3 is:

  • (0) = no problem
  • (1) = slight or mild intermittent problems
  • (2) = moderate, which are often present
  • (3) = severe, and life-disturbing problems

The rating scale for general somatic pain symptoms is:

  • (0) = no symptoms,
  • (1) = few symptoms,
  • (2) = a moderate number of symptoms and
  • (3) = a great deal of symptoms

The SS score ranges from 0-12.

Related Reading: Does Manual Therapy Massage Help Women with Fibromyalgia?

Clinical History and Examination Evidence Needed to Diagnose Fibromyalgia

The clinical history and examination evidence needed for this diagnosis includes (accordingly with the ACR diagnostic criteria):

  1. A widespread pain index (WPI) ≥ 7 and symptom severity (SS) scale score ≥ 5
  2. Alternatively a widespread pain index (WPI) 3 – 6 and SS scale score ≥ 9
  3. Symptoms have been present at a similar level for at least 3 months
  4. The patient does not have a disorder that would otherwise explain the pain

Myositis (ICD-10 M60.90)

This is moderately rare but it does occur when a recurring localized transient “non-infectious” idiopathic inflammation and sometimes swelling of the jaw closer muscle and connective tissues occurs.

When a diagnosis of myositis is suspected, it is necessary to rule out lymph adenopathy, salivary swelling, a local dental infection, a venous malformation or a systemic infection causing the swelling.

Myositis may occur spontaneously but it can develop due to trauma also.  A common cause of traumatic myositis is intramuscular injection of a carpule of local anesthetic, which also contains epinephrine, which is highly myotoxic.

Clinical History and Examination Evidence needed to Diagnose Myositis

  1. Swelling in the muscles
  2. No infectious cause is identified

Related Reading: How to Perform a TMJ Injection

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Like what you’re learning?  Consider enrolling in the Herman Ostrow School of Dentistry of USC’s online, competency-based 1-year certificate program or 3-year Master’s program in Orofacial Pain and Oral Medicine.


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Posted: December 14, 2020
<a href="" target="_self">Dr. Glenn Clark</a>

Dr. Glenn Clark

Glenn Clark, DDS, MS is an expert on sleep apnea, orofacial pain and oral medicine, and Temporomandibular Joint Disorder (TMJ). Dr. Clark serves as the Director for the Advanced Program in Orofacial Pain and Oral Medicine at the Herman Ostrow School of Dentistry of USC.

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