Atypical Spasmodic Dysphonia

Any discussion of atypical Spasmodic Dysphonia (SD) must begin with a recap of the typical features of SD: Spasmodic dysphonia is a focal laryngeal dystonia — a neurologically-based condition affecting voice production.

Common Forms of SD

• Adductory SD (most common):
  • Features: Strain and strangled voice, phonatory arrests (cut-outs, “catches,” or “grabs”)
• Abductory SD:
  • Features: Breathy voice, syllable dropouts to air or whisper

Both types can include dystonic vocal tremor.

Typical but not Universal Characteristics

• Worse with stress/fatigue
• Worse in chest register than falsetto
• Difficulty using voice on phones or in noisy environments
• May improve with alcohol
• Often better singing voice than speaking voice
• Does not affect breathing (phonation only)

6 Key Variants of Atypical Spasmodic Dysphonia (SD)

1. SD That “Leads with Tremor”

   • Presentation: Dominated by tremor (seems initially to be essential voice tremor)
   • Pitfall in the diagnostic process and protection from it: Spasms (adductory or abductory) may be infrequent or even subtle — and the examiner may overlook the dystonic features of the tremor: variability in tremor frequency (speed) and amplitude, or task-related changes.
   • Risk: Overlooking intermittent spasms, strain, or whispers, leading to misdiagnosis as pure essential tremor.

2. Tonic Variant of Adductory SD

   • Presentation: Continuous tightness/strain, but no obvious phonatory arrests.
   • Confusion Point: May misdiagnose as functional using the nonspecific diagnosis of muscle tension dysphonia (MTD).
   • Risk: In the history of expert opinion, phonatory arrests were once required for diagnosis, leading to misclassification and delays.

3. Voice Better on the Phone

   • Presentation: Unusually, the patient reports easier phone voice.
   • Confusion Point: This is very rare (fewer than 1 in 250 cases).
   • Risk: Clinician may dismiss SD diagnosis in favor of a “functional” diagnosis, due to this “inverted” pattern.

4. Singing Voice Worse Than Speaking

   • Presentation: Speaking is intact or nearly normal, but singing voice is severely impaired.
   • Confusion Point: Opposite of typical SD, where singing is often preserved.
   • Risk: May lead to a functional (mis-) diagnosis.

5. Pitch/Register SD

   • Presentation: Voice breaks at register shifts (e.g., chest to falsetto), without classic adduction or abduction features.
   • Mechanism Suggestion: Possible active spasms in the cricothyroid muscles combined with inhibitory spasms (going to “limp”) in the thyroarytenoid muscles.
   • Confusion Point: Since this is rare, perhaps 1 or 2 in 1500 cases, this may be misdiagnosed as “functional” or stress related.

6. SD (Phonatory) Combined with Respiratory Dystonia (Segmented Breathing)

   • Presentation: Spasms interfere with inspiratory or expiratory flow, creating “choppy” breath pattern.
   • Confusion Point: When seen alone, not a classic phonatory issue, but rather dystonia affecting respiration.
   • Risk: Can be mistaken for asthma or paradoxical vocal fold motion (PVFM) leading to unnecessary pulmonary consultation and testing.

Clinical Implications

Misdiagnosis is common in atypical SD, often as:

• Muscle tension dysphonia (MTD) due to unfamiliarity with tonic-variant SD;
• Essential tremor due to poor recognition of dystonic features and occasional spasms;
• Functional voice disorder;
• Psychogenic voice loss.

Key for clinicians:

• Use task-specific assessments (speaking vs. singing, reading vs. conversation, trial therapy).
• Look for dystonic features manifesting as both spasm and tremor or pitch-register breaks.

Atypical SD is still SD — just in disguise. Recognition depends on nuanced listening, careful vocal task elicitation and response analysis, and avoiding overreliance on “classic” features like phonatory arrest or speaking-only dysfunction.