What is the differential diagnosis for a patient presenting with slurred speech?

Differential Diagnosis for Slurred Speech

Slurred speech (dysarthria) requires immediate evaluation for stroke, severe electrolyte abnormalities, and other neurological emergencies, followed by systematic assessment for structural, neurological, and medication-related causes.

Life-Threatening Causes Requiring Immediate Evaluation

Acute Stroke

• Stroke is the most critical diagnosis to exclude when a patient presents with new-onset slurred speech, as it represents a time-sensitive emergency where treatment within hours can prevent permanent disability and death 1, 2, 3
• Dysarthria in stroke patients manifests as slurred but intelligible speech (mild-moderate) or unintelligible speech (severe), and is scored on the NIH Stroke Scale to quantify neurologic deficits 2
• Stroke can cause dysarthria through damage to muscles controlling speech or through damage to motor cortex areas controlling speech production 3

Severe Electrolyte Abnormalities

• Severe hyponatremia (sodium <100 mmol/L) can present with stroke-like symptoms including slurred speech, facial droop, and confusion that are completely reversible with sodium correction 4
• This is a critical pitfall: patients may be misdiagnosed as having stroke when the underlying cause is metabolic and fully correctable 4

Neurological Causes

Vocal Fold Paralysis

• Vocal fold paralysis from recurrent laryngeal nerve damage causes dysphonia (altered voice quality) rather than true dysarthria, but patients may describe this as "slurred speech" 5, 6
• Common causes include post-thyroid surgery (up to 2.1%), cervical anterior surgery (1.69-24.2%), prolonged intubation (up to 94%), and tumors compressing the recurrent laryngeal nerve 6
• The left recurrent laryngeal nerve is more commonly affected due to its longer path around the aortic arch 6

Progressive Neurodegenerative Disorders

• Corticobasal degeneration and atypical progressive supranuclear palsy can present with progressive speech disturbance as the initial symptom, followed by bradykinesia, dementia, and vertical gaze palsy 7
• Parkinson's disease increases risk of dysphonia and dysarthria through multiple mechanisms 6

Structural Laryngeal Causes

Laryngeal Pathology

• Head and neck cancer is the most critical diagnosis to exclude in patients with persistent voice changes, as delayed diagnosis results in higher staging, more aggressive treatment requirements, and reduced survival 6
• Smoking increases odds of head and neck cancer 2-3 fold and is the strongest risk factor for malignancy 6
• Vocal cord nodules represent 77% of causes of dysphonia in children and develop mainly due to vocal abuse 6

Medication-Related Causes

Common Culprits

• Inhaled steroids cause dose-dependent mucosal irritation and fungal laryngitis 6
• ACE inhibitors cause chronic cough leading to voice changes 6
• Antihistamines, diuretics, and anticholinergics cause drying effect on mucosa 6

Infectious and Inflammatory Causes

Acute Viral Laryngitis

• Viral upper respiratory tract infection is the most common cause of acute dysphonia, typically self-limited and resolving in 7-10 days (1-3 weeks maximum) 1, 6
• Initial observation for most patients with new-onset dysphonia is reasonable if no red flags are present 1

Aspiration Risk Assessment

Dysphagia and Aspiration

• Patients with slurred speech (dysarthria) are at high risk for aspiration and should be evaluated for oral-pharyngeal dysphagia, as dysarthria is characterized by slowed or slurred speech resulting in reduced intelligibility and often coexists with swallowing dysfunction 1
• Patients with reduced level of consciousness are at high risk for aspiration and should not be fed orally until consciousness improves 1
• Alert patients with slurred speech should be observed drinking small amounts of water (3 oz); if they cough or show clinical signs of aspiration (wet voice, throat clear, hoarse voice after swallowing), they should be referred for detailed swallowing evaluation, preferably to a speech-language pathologist 1

Diagnostic Algorithm

Immediate Assessment (Within Minutes to Hours)

• Assess for stroke symptoms: facial droop, arm weakness, time of onset 2, 4
• Check serum sodium and other electrolytes immediately to rule out severe hyponatremia 4
• Evaluate level of consciousness and aspiration risk 1

Early Assessment (Within Days)

• If hoarseness/dysphonia persists beyond 1-3 weeks or if serious underlying cause suspected, perform laryngoscopy or refer to otolaryngology 1, 5
• Red flags requiring expedited laryngeal evaluation include: recent head/neck/chest surgery, recent intubation, concomitant neck mass, respiratory distress, tobacco/alcohol abuse, hemoptysis, dysphagia, odynophagia, otalgia, unexplained weight loss, or progressive worsening 5

Critical Pitfalls to Avoid

• Do not delay laryngoscopy beyond 4 weeks in persistent hoarseness 5
• Do not prescribe antibiotics, corticosteroids, or proton pump inhibitors empirically without visualizing the larynx first 5
• Do not obtain CT or MRI before performing laryngoscopy—imaging should only follow direct visualization 1, 5
• Do not miss severe hyponatremia by assuming all slurred speech is stroke 4
• Delaying otolaryngology referral beyond 3 months more than doubles healthcare costs ($271 to $711) and risks missing critical diagnoses including laryngeal cancer, vocal fold paralysis, and benign vocal fold pathology 5