Spasmodic dysphonia affects the laryngeal muscles causing involuntary and sustained muscle contraction. Patients with isolated spasmodic dysphonia have an approximate 7% risk that dystonia may spread to another body part.  Patients with spasmodic dysphonia are more likely to have associated tremor. As with many forms of focal dystonia, isolated voice tremor is most suggestive of laryngeal dystonia/spasmodic dysphonia¹. 
In all types of laryngeal dystonia, the dystonic muscles contractions are task specific usually affecting speech while sparing other laryngeal tasks such as breathing, singing, swallowing or coughing. Similar to other focal dystonias, sensory tricks such as humming are effective in reducing the dystonic movement.

The condition can involve the larynx alone, or it can be associated with a spectrum of head and neck dystonias such as blepharospasm, torticollis, hemifacial spasm, cervical dystonia, and Meige syndrome (blepharospasm and oromandibular dystonia).

Patients with dystonic vocal tremors cannot change pitch during vocalization, and performing this manoeuvre can aide in the bedside diagnosis. A sustained phonatory vowel task carried out with fibreoptic examination of pharyngeal and laryngeal musculature, supplemented by acoustic measures can help to characterize and confirm the nature of the tremor¹.

Spasmodic dysphonia can encompass a variety of clinical manifestations, sometimes including a tremor component.
The presentation may be that of an adductor-type or an abductor-type dystonia.

• Adductor type dysphonia is a voice disorder characterized by an effortful, strained, strangulated voice quality associated with intermittent voice stoppages, or phonatory breaks associated with over-adduction/closure of the vocal folds or vocal cords.  The voice is typically worse when speaking and may improve with singing, whispering, shouting or changing pitch. The condition usually presents in the fifth decade with a slight female predominance.

• Abductor spasmodic dysphonia manifests as a whispery voice, with intermittent breathy breaks due to prolonged abduction of the vocal folds during voiceless consonants in speech. This is due to spasm of the posterior cricoarytenoid muscle, the only abductor muscle of the larynx^2,3.

(vv)Dysphonia.mp4(tt)

From; Brin MF, Blitzer A, Fahn S, Gould W, Lovelace RE. Adductor laryngeal dystonia (spastic dysphonia): treatment with local injections of botulinum toxin (Botox). Mov Disord. 1989;4(4):287-96. 

Examination

Adductor dysphonia:
The spasms are best elicited when the vocal folds are approximating, for example, with vowels and voiced consonants such as /b/, /d/, /g/, and /m/.

Vocal tasks:

• We eat apples and eggs
• We mow our lawn all year
• A dog dug a new bone
• We eat eels everyday
• Counting from 80 to 90
• Sustained “E”

Abductor dysphonia

The involuntary opening of the vocal folds causes excessive airflow to escape and loss of vocalization. Patients have difficulty with /h/, /s/, /f/, /P/, /t/, and /k/. The breathy interruptions in speech commonly occur when going from unvoiced consonant to a voiced phoneme or vowel. For the tasks below, listeners would hear “Puheeter will kuheep at the puheek” when patients read, “Peter will keep at the peak,” or “sahixty” when saying “sixty.

Vocal Tasks:

• Harry hit the hammer hard
• The puppy bit the tape
• Peter will keep at the peak
• Six sassy mice raced across the ice
• The hunter hides in the hut
• Counting from 60 to 85

Voice tremor

Voice tremor is a feature of a number of neurological conditions, including PD, ET, and ataxia, as well as spasmodic dystonia.
In dystonia, voice tremor may be observed in DYT-THAP1 and DYT-ANO3 mutation carriers.

With respect to definition, although experts in dystonia may distinguish between irregular/jerky and regular/sinusoidal tremor of the limbs, this does not hold true for voice tremor, because voice experts do not traditionally acknowledge a voice tremor that is predominantly irregular/jerky. Cases where the movement is predominantly irregular/jerky are typically diagnosed as having spasmodic dysphonia, and not tremor⁴.

Tremor of the voice due to essential tremor(ET) is more common in women and appears most frequently in the seventh decade.  Patients with ET commonly complained of challenges maintaining voice volume and of increased phonatory effort⁵.
Laryngeal tremor is present in about 25% of patients with any type of ET and in 50% of patients with head tremor. However, patients can also have isolated laryngeal tremor, although this is most suggestive of spasmodic dysphonia. The voice may have a shaky or quavering quality, and tremor may be mistaken for spasmodic dysphonia because muscular tremors can mimic glottic stops.

Examination

Sustained phonation: tremor may be present with sustained phonation due to ET, which is not present with spasmodic dystonia.

Adductor spasmodic dysphonia is provoked by phrases containing many voiced onsets (eg, counting from 80 to 90), whereas the voice of patients with voice tremor from ET will be affected across all voice tasks without regard to phonetic composition.

Patients with dystonic vocal tremors cannot change pitch during vocalization, and performing this manoeuvre can aid in the bedside diagnosis (see Dystonic Tremor).   Dystonic patients are more likely to have reduction of tremor in the palate, pharynx, and larynx  when using a higher “falsetto” pitch⁴.

Laryngoscopy of ET patients with vocal tremor shows an entrained, oscillatory motion of several anatomic structures during sustained phonation. Many patients have oscillatory movements during quiet respiration. Tremor can involve muscles of the palate, pharynx, tongue, and other articulatory muscles in addition to the larynx. This distribution does not distinguish vocal tremor due to ET from spasmodic dysphonia.

Laryngeal Anatomy

Muscle tension dysphonia (MTD)

MTD describes voice disorders caused by poorly regulated or abnormal laryngeal movements during phonation³.
Other frequently used terms include muscle misuse, hyperfunctional dysphonia, and tension-fatigue syndrome. There is hypercontraction or excessive tension in the intrinsic and/or extrinsic musculature. Individuals with MTD have a more evenly produced strained or breathy voice that is consistently present throughout all vocal tasks. They frequently lack the predictable breaks in targeted phonemes, and symptoms can wax and wane.
MTD may also be a compensatory mechanism for spasmodic dysphonia as the patient strains to produce desired phonemes. Similarly to  spasmodic dysphonia, patients may still be able to sing, cough, and cry without difficulty.

Treatment predominately rests with voice therapy, and some patients may benefit from psychiatric evaluation to address emotional stressors that often contribute to MTD.
A trial of voice therapy can be helpful to unload any vocal strain when trying to differentiate MTD from  spasmodic dysphonia.

Functional dysphonia can be considered a subtype of MTD. Patients may mimic strained or aphonic voice issues such as those present in spasmodic dysphonia . Treatment resides in voice therapy and psychiatric intervention.

Treatment

Botulinum toxin is the standard treatment for spasmodic dysphonia.
In patients with abductor forms, the treatment results are less favourable.

Side effects include hoarseness, breathiness of voice and hypophonia. Adverse effects may also include difficulties with swallowing liquids or solid food. Other side effects include weakness of coughing and some pain at the injection side, and dyspnea may result .

In adductor forms, 5 units of Botox are administered into the thyroarytenoid muscles bilaterally. Typically bilateral injections are given; if adverse events, a unilateral injection may be tried.

In abductor forms, 5 units of Botox are administered into the posterior cricoarytenoid muscle unilaterally in order to avoid dyspnea. BT application can be performed perorally or transcutaneously using electromyographic guidance⁶.   Since the posterior cricoarytenoid muscle is the only abductor of the vocal folds, over injection of botulism can result in the inability to abduct the vocal folds during inspiration causing stridor and dyspnea. Therefore, unilateral injection of the posterior cricoarytenoid muscle that appears to have the greatest spasm on laryngoscopy is performed.

EMG

• Adductor laryngeal dystonia has abnormally high activity in the thyroartenoid and cricothyroid muscles.
• Abductor laryngeal dystonia has abnormally high activity in the posterior cricoarytenoid and thyroaryentoid.