Dysarthria is a disorder of the speech which is characterized by poorly articulated speech that is presented with irregular and laboured rhythm of the speech. It is associated with palate weakness that is presented with a nasal voice tone. Dysarthria is detected in ordinary conversation. Dysarthria may occur gradually and abruptly. Patient with dysarthria is finding it difficult to make sounds or words such as “cat”, “sh” and “ba”. It is a confirmation test. Dysarthria may sometimes be confused with aphasia. Aphasia is a speech disorder that is divided into receptive aphasia (inability to comprehend and understand speech) and expressive aphasia (inability to initiate the speech and express themselves). Dysarthria occurs due to olivopontocerebellar degeneration (classical sign). Dysarthria is associated with degenerative neurological disorders. Dysarthria may also occur due to damage to the brainstem which affects the ninth cranial nerve, tenth cranial nerve and eleventh cranial nerve. An ill fitting denture may also result in dysarthria.
Patient with dysarthria may require a series of assessment that include the history and examination. The patient is asked about any history of TIA /transient ischaemic attack or stroke, the onset of dysarthria, the part of the day when dysarthria is the worst, the impairment of the speech due to TIA or stroke, past history of seizures, history of drugs or excessive alcohol intake and the timeline when dysarthria begin, worse and relief.
The common causes of dysarthria may include Shy Drager syndrome, olivopontocerebellar degeneration, Myasthenia Gravis, poisoning, Parkinson disease, multiple sclerosis, cerebral cerebrovascular accident, brainstem cerebrovascular accident, botulism, basilar artery insufficiency, amyotrophic lateral sclerosis and alcohol cerebellar degeneration.
Shy Drager Syndrome is presented with dysarthria, chronic orthostatic hypotension, cerebellar ataxia, incontinence, stooped posture, impotence, dementia, mask-like faces and bradykinesia.
Cerebellar ataxia, dysarthria and spasticity are a major sign of olivopontocerebellar degeneration.
Myasthenia Gravis is presented with dysarthria which is worse during the day. Dysarthria is usually accompanied with nasal voice tone in case of myasthenia Gravis. Another finding of myasthenia Gravis may include facial weakness, drooling, diplopia, dysphagia, dyspnea, muscle weakness and ptosis.
Progressive dysarthria that presented with limb stiffness, hand tremor, drooling, hallucination, confusion, fatigue, weakness, propulsive gait, gross rhythmic movement of the hand and trunk and spasticity are the signs of manganese poisoning. Tremors, ataxia, confusion, irritability , lethargy, depression, fatigue and weakness as well as progressive dysarthria may also occur due to mercury poisoning.
Parkinson’s disease is presented with monotonic voice, dysarthria, bradykinesia, stooped posture, muscle weakness, difficulty walking, involuntary tremor that begin in the finger, muscle rigidity, drooling (occasionally), dysphagia and mask- like faces.
Multiple sclerosis is associated with demyelination of the cerebellum and brainstem. This condition is associated with dysarthria, intention tremor, ataxia, dysphagia, double or blurred vision and nystagmus. The patient may also present with incontinence, urgency, urinary frequency, emotional lability, constipation, muscle paralysis, weakness, hyperreflexia, spasticity and paraesthesia. The remission and exacerbation of the symptoms may occur.
Cerebral cerebrovascular accident is another condition that may lead to dysarthria. The cerebral cerebrovascular accident is a massive bilateral cerebrovascular accident that leads to pseudobulbar palsy. The dysarthria is caused by a bilateral weakness which is also accompanied by aphasia, bilateral hemianopia, dysphonia, drooling, dysphagia, hyperreflexia, spasticity and sensory loss.
Brainstem cerebrovascular accidents may present with dysarthria which is severe during the onset and disappear after rehabilitation. Brainstem cerebrovascular accident is characterized by the presence of bulbar palsy. The bulbar palsy is characterized by the triad of dysphagia, dysphonia and dysarthria. The patient may also present with loss of consciousness, dyspnea, drooling, spasticity, hemiparesis, diplopia and facial weakness.
Botulism may initially present with diarrhoea, vomiting, weakness, sore throat and dry mouth. This will later follow by descending paralysis or weakness of the muscle in the trunk and the extremities which cause dyspnea and hyporeflexia. Botulism is associated with cranial nerve dysfunction that present with ptosis, diplopia, dysphagia and dysarthria.
Basilar artery insufficiency is a disorder which causes dysarthria as a result of brief random episodes of bilateral brainstem dysfunction. Basilar artery insufficiency may accompany with the signs and symptoms such as visual field loss, paresis, ataxia, facial numbness, vertigo and diplopia which last from minutes to hours.
The signs and symptoms of amyotrophic lateral sclerosis may include dysarthria that occurs due to the involvement of the bulbar nuclei that is worsening as the disease progress, muscle atrophy and weakness (feet and hand), spasticity, fasciculations, difficulty breathing, hyperactive deep tendon reflexes in the leg, dysphagia and excessive drooling. Inappropriate laughter and crying spell may occur as a result of progressive bulbar palsy.
Alcohol cerebellar degeneration is a progressive neurodegenerative disorder that presented with progressive chronic dysarthria and hypotension, diplopia, altered mental status, ophthalmoplegia and ataxia.
There are certain drugs that may cause dysarthria which include ingestion of a high dose of anticonvulsant and high dose of barbiturates.
Slow growing tumour such as brainstem glioma may cause dysarthria. Brainstem glioma is a tumour that primarily affects children. Cerebral palsy may also present with dysarthria. On examination, patient’s neurological deficit is checked and in infant or children, dysarthria is difficult to detect based on the fact that speech has not been perfected completely.
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