Voice disorders represent an area of communication dysfunctions, which affects a large population of people. Individuals with voice disorders range from a simple case of laryngitis that usually resolves spontaneously to more physical or organic conditions such as laryngeal malignancy.

Symptoms

The main symptom in people with voice disorders is hoarseness or dysphonia, which describes an alteration in voice quality. It is difficult to define a normal or an abnormal voice quality in the absence of a fixed, uniform standard of abnormal voice but according to Aronson (1990) ‘a voice disorder exists when quality, pitch, loudness or flexibility differs from the voices of others of similar age, sex and cultural group’. A voice disorder may also exist when the structure of the laryngeal mechanism, the function, or both no longer meet the voicing requirements of the speaker (Stemple et al., 2000). In medical practice, hoarseness is described as a symptom of laryngeal disorder, which is often the first and only signal of disease, local or systemic, involving this area. The differential diagnosis is important as many different medical and surgical conditions may result in hoarseness.

Aetiology

Voice disorders can be aetiologically classified into organic and non-organic types; the latter are often referred to as functional or psychogenic types. In organic voice disorders, the faulty voice is caused by structural or physical disease of the larynx itself, or by systemic illness that alters laryngeal structure (Boone & McFarlane, 1988).

Myasthenia gravis

Myasthenia gravis is a neurological disease which is characterized by abnormal muscle fatigability. It may affect any group of muscles; head and neck muscles are initially most affected, with extraocular muscles most commonly involved (Stell, 1987). The disease is relatively rare, with an incidence between 2 and 10 per 100 000 (Garfinkle & Kimmelman, 1982). This condition occurs in all ages, but is usually seen in young adults and is twice as common in women as men. Onset for females is reported in the third decade of life, while in males it is during the sixth decade (Garfinkle & Kimmelman, 1982). Aetiology is unknown, but current evidence suggests that it is an autoimmune disease attributed to a decrease in the number of acetylcholine receptors in the motor end plate (Fritze et al., 1974).

Patients with myasthenia gravis tend to show bulbar symptoms, with the initial and most common being drooping of the eyelids or ptosis (Grob, 1961). They also report dysarthria characterized by hypernasality, reduced loudness, increased breathiness and articulatory imprecision (Aronson, 1990), dysphagia, diplopia, weakness of the legs and blurred vision. The unique features of myasthenia gravis are fatigability, fluctuation of function and restoration of function after rest (Colton & Casper, 1990). Diagnosis depends on the typical clinical picture and can be confirmed by intravenous administration of edrophonium (Tensilon Test), laryngeal electromyographic measurements or detection of anti-acetylcholine receptor antibodies in the blood.