Spasmodic Dysphonia

Spasmodic dysphonia (laryngeal dystonia) is a focal, task specific laryngeal dystonia that affects speech. It is characterised by involuntary spasms of the intrinsic laryngeal muscles during phonation (but not during whispering, laughing, singing, or crying), producing strained, strangled, or breathy voice breaks.

Prevalence is about 1 per 100,000 (up to 4 per 100,000), with onset typically in the fourth to fifth decade and a female predominance (about 2:1).

The cause is unknown but involves abnormal basal ganglia, thalamic and sensorimotor cortical processing with a neurogenic basis (impaired inhibition of the central laryngeal motor network). Genetic factors (family history in about 12 percent, with THAP1 and other mutations in some) and environmental triggers (upper respiratory infection, voice overuse, stress or trauma) have been suggested, though they are not causal.

Types:

• Adductor spasmodic dysphonia (about 80 to 90 percent): spasms of the thyroarytenoid and lateral cricoarytenoid cause sudden vocal fold hyperadduction. This produces a strained strangled voice with voice breaks, particularly on vowels.
• Abductor spasmodic dysphonia (10 to 15 percent): spasms of the posterior cricoarytenoid cause sudden vocal fold abduction with breathy voice breaks, particularly on voiceless consonants.
• Mixed or adductor with tremor (vocal tremor in 30 to 40 percent).

It is not a psychological disorder, though stress can worsen it. It often coexists with other dystonias (blepharospasm, oromandibular, cervical dystonia, or essential tremor).

• Insidious onset of effortful, strained, strangled voice with intermittent voice breaks (adductor) or breathy, whispery voice breaks (abductor). It worsens with stress, phone conversations, and connected speech.
• It improves with whispering, singing, shouting, laughter, yawning, speaking in a high pitched voice, or with tilted head, and in some, after alcohol.
• Voice quality is normal in non-speech vocalisation, and the symptoms are task specific, with variable severity over time and across situations (variability is typical, and worse in tension).
• Voice fatigue, throat tension and effort in speaking, and social and occupational impairment, with anxiety and depression.
• Vocal tremor may be present (a 4 to 7 Hz oscillation).
• Examination: normal laryngeal anatomy at rest, with an intact vocal fold mobility on flexible laryngoscopy; during connected speech: sudden spasm in adductor type (vocal fold hyperadduction with supraglottic compression), and abductor spasm in abductor type.
• Neurological examination to detect other dystonic features, and signs of Parkinson disease or essential tremor.

• Diagnosis is clinical: perceptual voice analysis during connected speech (sentences with voiced phonemes for adductor, and unvoiced consonants for abductor, such as "we mow our lawn all year" and "Harry has a pet kitten"), combined with the history, and the presence of task specificity.
• Flexible fibreoptic laryngoscopy with videostroboscopy during sustained vowels, whispered speech and connected speech: to exclude structural abnormalities and vocal fold paralysis, and show the spasm patterns; typically a normal structure at rest.
• Multidisciplinary voice evaluation by otolaryngologist, speech language pathologist and neurologist; acoustic and aerodynamic analyses; laryngeal electromyography (to confirm dystonic activity: involuntary spasms of the thyroarytenoid or posterior cricoarytenoid muscles, and to guide botulinum toxin injection).
• Differential diagnosis: muscle tension dysphonia (the commonest mimic, with improvement with voice therapy), vocal tremor, vocal fold paralysis, Parkinson disease, vocal fold lesions, laryngopharyngeal reflux, psychogenic dysphonia, and neurological disorders (such as cerebellar disease and bulbar disease).
• MRI brain is considered if neurological signs are present.

There is no cure; symptomatic treatment with botulinum toxin is the standard of care.

• Botulinum toxin A injections (onabotulinumtoxinA, abobotulinumtoxinA, or incobotulinumtoxinA) into the laryngeal muscles, repeated every 3 to 6 months. They produce improvement in about 90 percent (sustained improvement of voice by 70 to 90 percent for about 3 to 4 months).
• Adductor type: bilateral thyroarytenoid (with or without lateral cricoarytenoid) injections via a percutaneous (transcutaneous through the cricothyroid membrane under EMG guidance) or transoral (indirect or flexible endoscopic) route. The dose is low, 1 to 2.5 units onabotulinumtoxinA per side (bilateral), or 2.5 units unilateral.
• Effects begin in 2 to 3 days and peak within 1 to 2 weeks. Typical side effects are breathy voice (in 2 to 3 weeks, in 10 to 30 percent) and aspiration of liquids and choking, which are transient. The lowest effective dose is therefore used and titrated.
• Abductor type: posterior cricoarytenoid injection (unilateral, 3.75 to 5 units, and the opposite side after 1 to 2 weeks if needed). There is a risk of stridor and airway compromise, so bilateral injection requires caution.
• Tremor: thyroarytenoid injection with adjuncts.
• Voice therapy (speech language pathology): used as an adjunct to botulinum toxin (not as a primary treatment), by training breath support, relaxation, techniques to reduce vocal effort, and improving the voice quality, and speech strategies; Not curative.
• Oral medications (limited, modest benefit, mostly in patients with tremor or who cannot get injections): benzodiazepines (clonazepam 0.5 to 2 mg daily), anticholinergics (trihexyphenidyl 2 to 15 mg daily in divided doses), baclofen 10 to 60 mg daily, propranolol 10 to 40 mg two to three times daily for voice tremor, primidone 25 to 250 mg daily for tremor, and sodium oxybate (limited).
• Surgical options for adductor spasmodic dysphonia (for patients with inadequate or intolerable response to botulinum toxin):
  • selective laryngeal adductor denervation reinnervation (SLAD-R; section of the adductor branch of the recurrent laryngeal nerve, and reinnervation with the ansa cervicalis branch, with 70 to 90 percent improvement for several years)
  • type 2 thyroplasty (laryngeal framework surgery with a titanium bridge to widen the glottis)
  • thyroarytenoid myectomy
  Recurrent laryngeal nerve section (historically) has a high failure rate. Deep brain stimulation is investigational, for refractory cases or with other dystonias.
• Psychological support (counselling, treatment of anxiety and depression) and patient support organisations.
• Follow up: every 3 to 6 months for botulinum toxin injection, with assessment of the voice outcomes (patient reported scales such as the Voice Handicap Index, and the Vocal Effort Rating), with dose adjustments.
• Prognosis: chronic, lifelong, but non-progressive and not life limiting; most patients can maintain good voice function with ongoing treatment.