A common cause of voice problems is abnormal patterns of muscle activation, referred to by many names, including muscle misuse dysphonia, vocal hyperfunction, or muscle tension dysphonia (MTD). To understand MTD, we must remember that voice production requires rapid and precise coordination of many muscles.
The degree of muscle contraction ("tension" setting), the timing of the contraction and the coordination of that activity with the simultaneous contraction of many other muscles, is an intricate and ever-changeable process that must be balanced with regulation of changing airflows and air pressures.
This balance of aerodynamic and muscle forces must adapt to rapidly changing speech requirements, including modulations of pitch, loudness, and rate, that are a component of all speech contexts. When an imbalance of muscle activity occurs during phonation, the result can be a range of symptoms from vocal fatigue, neck discomfort, altered vocal quality, to complete loss of voice.
There are many theories about the nature and causes of MTD, but little is known for certain, and MTD may vary among individuals. One theory is that the underlying mechanism of MTD is incomplete relaxation of the posterior cricoarytenoid muscle, the muscle responsible for opening the vocal folds. This may result in incomplete opening of the vocal folds during each vibratory cycle of phonation, which in turn causes the thyroarytenoid muscle (the body of the vocal folds) to over-contract in compensation.
Other theories describe the nature of MTD as excessive contraction of groups of intrinsic laryngeal muscles (the muscles of the vocal folds and those that connect the vocal folds and cartilages) and extrinsic laryngeal muscles (the muscles that connect parts of the larynx to other structures). Still another theory describes MTD as in-coordination of laryngeal muscle contraction with breathing, especially the amount of air pressure and the timing of the airflow.
It is unclear whether MTD represents a disorder primarily of incoordination (mis-timing) of muscles, or excessive muscle contraction. In either case, it can result in impaired vocal fold vibration and the sensation of extra effort when talking. Our inability to accurately measure the timing or force of laryngeal muscle contractions within a clinical setting contributes to our lack of clear understanding of this voice disorder.
The vocal tract above the true vocal folds in constricted, making it difficult to produce voice.
The cause of muscle tension dysphonia is not known. We hypothesize that it may be caused by the body's voice production system reacting to environmental (external) or systemic (internal) irritants. Common irritants include upper respiratory infection, second-hand smoke, laryngopharyngeal reflux (LPR), significant vocal demands, or stressful life events. Most often, it is likely more than one single factor. But truthfully, we do not yet understand why some people are susceptible to MTD and others are not.
MTD is sometimes categorized as either primary or secondary. In primary MTD, there is no clear or predominant organic cause (that is, no detectable abnormality of the structures or functioning of the larynx other than the MTD). Historically, MTD was called "functional" dysphonia, because the cause was unknown. However, that term often implied that there was no "real" reason for the problem and it was assumed to be a psychosomatic disorder. Although psychological factors may certainly contribute to MTD, we no longer feel it is primarily a psychosomatic problem.
In some cases of primary MTD, the factor which initially caused the abnormal muscle patterns (the precipitating cause) is no longer present, but the aberrant muscle behaviors have become a habit. We think this may occur, for example, in cases of upper respiratory infection, especially in speakers with significant vocal demands, such as teachers. In secondary MTD, the abnormal patterns of muscle activation are secondary to (a result of) another underlying disorder, such as vocal fold atrophy, or a benign lesion.
We think that, in an attempt to compensate for the vocal changes, an individual alters muscle activation patterns, possibly by using excessive muscle tension or recruiting the use of muscle not ordinarily active. This process is referred to as "maladaptive compensatory behaviors", and they can become a habit over time. In either primary or secondary MTD, the habitual use of abnormal patterns of muscle activation during phonation can be difficult to unlock without treatment.
The most common treatment for MTD is voice therapy. There are a number of different therapeutic regimens that improve voice production, including resonant voice techniques and digital laryngeal massage. Sometimes, the therapy program is intensive for the first week or two (up to three or four session in a week) and then quickly tapers off to once a week and then less frequently.
Although we have no research studies that prove the effectiveness of voice therapy for MTD, our clinical experience suggests that voice therapy is quite helpful, even in severe cases in which a person has almost no voice at all. Uncommonly, Botulinum toxin A ("botox") injections are used in conjunction with voice therapy. to release the abnormal muscle activation patterns.