Dysarthria is a speech disorder characterized by difficulty articulating words due to muscle weakness or poor control of the speech muscles. While various neurological conditions can cause dysarthria, certain medications can also induce or worsen this condition by affecting the brain, nervous system, or speech muscles. This article identifies specific medication classes that contribute to its development.
Understanding Dysarthria
Dysarthria is a motor speech disorder that arises from damage to the parts of the nervous system controlling the muscles used for speaking. These muscles are located in the face, tongue, throat, and even those that regulate breathing. The condition does not affect a person’s ability to understand language or formulate thoughts, but rather the physical execution of speech.
Common symptoms include slurred or mumbled speech, slow speech, difficulty controlling voice volume, and changes in voice quality, which may sound uneven or strained. The specific presentation can vary depending on which parts of the nervous system are affected.
Medications Known to Cause Dysarthria
Many medications can impact speech by influencing the central nervous system or directly affecting muscle function. These effects are often dose-dependent and may resolve once the medication is stopped or adjusted. Several drug classes are commonly implicated in dysarthria.
Sedatives and hypnotics, such as benzodiazepines, are central nervous system depressants. They enhance gamma-aminobutyric acid (GABA) activity, reducing neuronal excitability and leading to sedation and muscle relaxation that can manifest as slurred speech. Examples like diazepam and clonazepam may cause drowsiness and impaired motor coordination affecting speech.
Anticonvulsants, used for seizure disorders, can affect speech. Phenytoin and carbamazepine are examples that may cause dysarthria, often described as slurred speech. These effects can relate to cerebellar dysfunction or neurological side effects like ataxia (impaired coordination) and drowsiness.
Antipsychotics, especially older generations, can induce dysarthria through extrapyramidal symptoms. These involuntary movement disorders stem from the drugs’ effects on brain dopamine pathways. Such symptoms include dystonia, involving involuntary muscle contractions that may affect speech muscles, leading to slurred or difficult-to-understand speech.
Muscle relaxants reduce spasms and stiffness, often by acting on the central nervous system. While beneficial for muscle pain, this generalized muscle relaxation can extend to speech muscles, resulting in slurred or unclear articulation. Common side effects include drowsiness, dizziness, and generalized weakness.
Opioids, primarily for pain relief, depress the central nervous system by binding to receptors in the brain and spinal cord. This slows messages between the brain and body, leading to slowed or slurred speech and reduced articulation. Sedation and respiratory depression also contribute to these speech changes.
Lithium, used for bipolar disorder, can cause dysarthria, especially at toxic levels. Lithium neurotoxicity can lead to cerebellar dysfunction, directly impacting coordination and speech articulation. Even at therapeutic levels, some individuals may experience speech difficulties.
Certain chemotherapy drugs can induce dysarthria as a neurotoxic side effect. High-dose cytarabine, for instance, causes cerebellar dysfunction, presenting with symptoms like dysarthria and scanning speech. Irinotecan has been linked to transient dysarthria during infusion, often resolving upon pausing treatment.
What to Do if Medications Cause Dysarthria
If you suspect your medication is causing or worsening dysarthria, consult a healthcare professional. Do not discontinue or alter your dosage without medical guidance. A thorough evaluation by a doctor, neurologist, or pharmacist is necessary to determine the underlying cause.
Healthcare providers can review your regimen, assess potential drug-induced dysarthria, and consider dose adjustments or alternative treatments. In many cases, medication-induced dysarthria can improve or resolve once the causative drug is stopped or its dosage modified. Speech therapy may also be recommended to manage symptoms and improve communication.