Dysarthria Types: A Complete SLP Reference

Dysarthria is a group of motor speech disorders caused by weakness, slowness, incoordination, or altered tone of the speech musculature. Unlike aphasia, language is intact — the problem is execution, not formulation. Unlike apraxia of speech, the underlying muscles themselves are neurologically impaired rather than mis-programmed.

The Mayo Clinic classification

Darley, Aronson, and Brown's perceptual studies produced the classification still used in clinics and on exams: each dysarthria type maps to a level of the motor system, and each has a distinctive perceptual signature.

Flaccid dysarthria — lower motor neuron

Lesion: cranial nerve nuclei or peripheral nerves (final common pathway). Hallmarks are hypernasality, breathy voice, nasal emission, and imprecise consonants. Muscles are weak and hypotonic with atrophy and fasciculations. Causes include myasthenia gravis, Guillain-Barré, bulbar palsy, and isolated cranial nerve injury. Which nerve is damaged predicts the symptom: X (vagus) → hypernasality and breathiness, XII (hypoglossal) → lingual imprecision, VII (facial) → labial imprecision.

Spastic dysarthria — bilateral upper motor neuron

Bilateral damage to the direct and indirect activation pathways. Speech is strained-strangled, slow, with harsh voice quality, monopitch, monoloudness, and imprecise consonants. Hyperactive gag and jaw jerk, pseudobulbar affect. Causes: bilateral strokes, primary lateral sclerosis, TBI.

Ataxic dysarthria — cerebellum

The signature is irregular articulatory breakdown and excess and equal stress, producing the classic "drunken," scanning speech. Prosody is disordered rather than simply reduced. Causes: cerebellar stroke, degeneration, alcohol-related damage.

Hypokinetic dysarthria — basal ganglia (Parkinson's)

The paradox type: reduced loudness, monopitch, monoloudness, breathy voice, and rushes of speech with inappropriate silences — the only dysarthria in which rate may be too fast. Repetitive phoneme use (palilalia) is common. Treatment of choice is LSVT LOUD, a high-effort, intensive program targeting vocal loudness with recalibration of effort perception.

Hyperkinetic dysarthria — basal ganglia with involuntary movement

Speech is disrupted by involuntary movements: chorea, dystonia, tremor, tics, or myoclonus. Prolonged intervals, variable rate, and sudden voice stoppages. Causes: Huntington's disease, dystonia, tardive dyskinesia. Spasmodic dysphonia is a focal laryngeal hyperkinesia; adductor type is treated with botulinum toxin injection.

Unilateral upper motor neuron dysarthria

Usually mild and often transient: imprecise consonants, mild harshness, slow rate. Common after a single unilateral stroke and frequently accompanied by central facial weakness and lingual weakness contralateral to the lesion.

Mixed dysarthria

Any combination. The classic board example is ALS: mixed spastic-flaccid. Multiple sclerosis commonly produces mixed ataxic-spastic. Wilson's disease produces mixed hypokinetic-spastic-ataxic.

The five speech subsystems

Assessment and treatment are organized by subsystem, not by diagnosis: respiration, phonation, resonance, articulation, and prosody. Determine which subsystem contributes most to reduced intelligibility, and treat there first. A patient with severe hypernasality gains more from a palatal lift than from articulation drill.

Assessment tools and measures

• Oral mechanism examination — strength, symmetry, range, rate, tone.
• Alternating and sequential motion rates (puh-puh-puh; puh-tuh-kuh) — ataxic speakers are irregular, spastic speakers are slow and strained, hypokinetic speakers accelerate or blur.
• Maximum phonation time and s/z ratio for laryngeal function.
• Intelligibility measures such as the Sentence Intelligibility Test; the Frenchay Dysarthria Assessment for subsystem profiling.

Treatment principles

Restorative approaches target physiology (respiratory support, effortful closure, loudness). Compensatory approaches change the speaking act (slowed rate, overarticulation, pausing, topic pre-announcement). Prosthetic and AAC options — palatal lifts, amplifiers, speech-generating devices — belong in the plan early for progressive disease, alongside message banking and voice banking before intelligibility declines.

Dysarthria vs. apraxia of speech

Dysarthria errors are consistent, distortion-heavy, and present across all speech tasks including automatic speech. Apraxia errors are inconsistent, substitution- and groping-heavy, worse with increasing word length, and often dramatically better on automatic speech. See our apraxia reference for the full differential.