Dysphagia After Stroke - Laterality

The Short Answer

What the Textbooks Say

"Strokes involving the right hemisphere tend to produce more impairment of pharyngeal motility, whereas left hemispheric lesions have a greater effect on oral stage function."

• Right hemisphere stroke - impairs the pharyngeal phase (involuntary, reflexive component of swallowing)
• Left hemisphere stroke - impairs the oral phase (voluntary, preparatory component)

Why This Happens: The Bihemispheric Representation Model

1. After unilateral stroke, dysphagia depends on whether the stroke hit the dominant swallowing hemisphere
2. Recovery depends on cortical reorganization in the contralesional (unaffected) hemisphere - patients who recover well show greater pharyngeal cortical representation in the unaffected hemisphere (Hamdy et al., confirmed in Adams & Victor)
3. Dysphagic patients post-stroke have a smaller pharyngeal representation in the unaffected hemisphere - meaning there is less "reserve" to compensate

Where Dysphagia is Most Severe

Important Caveats

• The common belief that dysphagia = brainstem stroke is a myth - it is well documented in cortical and subcortical hemispheric strokes too
• Dysphagia occurs in roughly 50% of all acute strokes in the first few days, on either side
• Subcortical strokes (internal capsule, basal ganglia) carry a higher incidence of dysphagia and aspiration than cortical ones
• Bilateral frontoparietal opercular damage causes Foix-Chavany-Marie syndrome - complete loss of volitional facial/tongue/pharyngeal movement with preserved involuntary movements

Bottom Line for Exams

Respiratory Patterns in Stroke - Localization Guide

1. Cheyne-Stokes Respiration

• Breathing slowly oscillates between hyperventilation and hypoventilation, with periods of apnea
• Classic crescendo-decrescendo pattern cycling roughly every 45-60 seconds
• Caused by bilateral lesions anywhere along the descending pathway from forebrain to upper pons
• Patients are more alert during the waxing phase and less alert during apnea
• A relatively good prognostic sign - implies no permanent brainstem damage
• Also seen in cardiac failure (prolonged circulation time)
• Warning: emergence in a patient with a unilateral mass lesion = early sign of herniation

2. Central Neurogenic Hyperventilation

• Sustained rapid breathing at 40-70 breaths/min
• Rare - must be distinguished from reactive hyperventilation from hypoxia or metabolic acidosis
• Large CNS lesions can cause neurogenic pulmonary edema with secondary hypoxemia that mimics this

3. Apneustic Breathing

• Prolonged inspiratory gasp with a pause at full inspiration (2-3 second hold)
• Caused by lesions of the medial parabrachial/Kolliker-Fuse area of the rostral pons
• Indicates pontine level damage

4. Cluster (Short-cycle Periodic) Breathing

• Periodic respirations irregular in frequency and amplitude, with variable pauses between clusters
• Short cycle (faster than Cheyne-Stokes), bursts of 7-10 rapid breaths then apnea, without waxing-waning prodrome
• Also seen with increased ICP and posterior fossa expanding lesions

5. Ataxic (Biot's) Breathing

• Completely irregular in both rate and rhythm - chaotic breathing
• Combination of ataxic respiration + bilateral 6th nerve palsy = warning sign of brainstem compression from posterior fossa expanding lesion
• Pre-terminal pattern - indicates severe lower brainstem damage
• Can progress abruptly to respiratory arrest

Summary Table

Important Points

• Progression from Cheyne-Stokes → central hyperventilation → apneustic → ataxic reflects rostrocaudal deterioration (transtentorial herniation progressing downward) - an ominous sign
• Medullary stroke (e.g., lateral medullary/Wallenberg) can cause respiratory arrest and death due to disruption of the automatic respiratory centers
• Subcortical/locked-in syndrome (midpontine stroke): automatic breathing preserved but voluntary breathing lost (can't voluntarily hyperventilate on command)
• Brainstem infarctions are the most life-threatening in terms of respiratory compromise