To be able to speak clearly, the muscles of the tongue, palate and lips, as well as the innervating peripheral nerves and corticobulbar tracts to the brainstem nuclei must be intact. In addition, the coordination of lip, tongue and palate movements must be unimpaired. This coordination is a function of the extrapyramidal system and the cerebellum. Speech impairment is known as dysarthria.
- Muscles, peripheral nerves (VII, IX, X and XII) and corticobulbar tracts.
For the examination, please refer to the section ‘The cranial nerves’. If these structures are affected, the speech will be nasal, and if the corticobulbar tracts are involved it is, slow and stuttering as well, with particular problems with sounds that are formed in the mouth (p, b, t, d). This speech impairment is easy to distinguish from stuttering, which is considered to be a development disorder. Stuttering is less consistently present. The ‘patient’ interchanges stuttering with sentences in which they do not stutter at all.
- The extrapyramidal system. A frequently-occurring extrapyramidal condition is Parkinson’s disease.
The diagnosis is usually not made on the basis of the patient’s speech disorder as this is not an early symptom of the disease. The patient will start to talk more quietly, more monotonously and articulation will become less clear.
- The cerebellum. The speech of patients with a diffuse cerebellar condition or one involving the cerebellar vermis becomes slow and stuttering. Sometimes so-called dysmetric articulation movements are seen. The patient appears to grimace when talking. In general, it remains easy to understand the patient.