We thank Dr. Friedman for his interest in our article. However, we disagree with his comment that masticatory myospasm is common. This is a long-held belief not supported by the literature.
Myospasm is an acute disorder characterized by sudden, involuntary, tonic contraction of the muscle.1 During a spasm, the muscle is acutely shortened, painful and with limitation in range of movement. It is diagnosed by use of needle electromyography (EMG), which will reveal sustained involuntary muscle contraction even at rest.1 A simple analogy is a cramp of the toe or calf.
Moreover, based on the "pain adaptation model," muscle pain is rarely a continuous negative phenomenon as seen in orofacial movement disorders; rather, it has an adaptive protective value to prevent further pain and dysfunction.2,3 Also, although the etiology of myospasm remains an enigma, it is likely centrally mediated rather than the result of a local temporomandibular joint disorder.
As for the myospasm’s being confused with other orofacial pains, a thorough history and examination should lead to the correct diagnosis. The secondary muscular condition that Dr. Friedman points to, which may occur in the presence of a constant deep pain input such as temporomandibular joint inflammation, dental trauma or persistent idiopathic facial pain (atypical facial pain), is likely masticatory muscle co-contraction and not myospasm.
With regard to the study Dr. Friedman cited, the conclusion of 77 percent of closed lock cases having muscle spasm (masticatory muscle hyperactivity, according to the study) is based on "symptomatic response to isometric force applied to the opening and closing jaw muscles." A symptomatic response to isometric force testing of muscle merely suggests masticatory myalgia. Given that needle EMG of the muscle in pain was not performed, the conclusion is not valid.4
We do agree with Dr. Friedman that restriction of jaw range of movement can be the result of inflammation, and this is likely due to the patient’s avoidance of pain. However, marked restriction such as a less-than-20–millimeter opening is likely due to muscle co-contraction.2 Once again, careful history taking and examination will differentiate the intracapsular and extracapsular sources of pain.
We acknowledge that muscle palpation can be misleading because, for example, "several structures overlie the masseter muscle." However, this is the best tool we currently have to differentiate between the source of pain and site of pain. We disagree with Dr. Friedman that muscle palpation does not distinguish between local muscle pain and referred pain. In fact, this is a basic principle to differentiate the two. Local provocation of the source of pain (local muscle pain) will elicit a pain response. However, local provocation of the site of pain may not elicit a pain response.5
As Dr. Friedman stated, the inferior lateral pterygoid muscle cannot be palpated, and hence it is examined by means of isometric force applied to the jaw. However, we disagree with his comments: "Except in some trauma cases, masticatory myospasm usually occurs gradually and is rarely painful at rest. This condition can be identified easily by means of muscle testing." In many trauma cases, the muscle is in co-contraction, and this condition is often misdiagnosed as muscle spasm. Also, "muscle testing" does not differentiate between the different muscle pains. Therefore, pain upon muscle testing may merely suggest a local muscle soreness or myofascial pain (trigger point) and not myospasm.
In summary, masticatory muscle spasm is not common. A positive response to resistive muscle tests alone is not diagnostic for masticatory muscle spasm. Also, a single test result rarely leads to a diagnosis in the field of orofacial pain. Hence, the combination of a thorough history and examination is required to establish the correct diagnosis.
TOP
References
