## Distinguishing RLN vs SLN Injury ### Clinical Presentation Comparison | Feature | RLN Injury | SLN Injury | |---------|-----------|----------| | **Voice quality** | Hoarse, breathy, weak | High-pitched loss, vocal fatigue | | **Vocal cord position** | Paramedian (abducted) | Normal position | | **Voice projection** | Severely reduced | Maintained but fatigable | | **Stridor** | Present (bilateral injury) | Absent | | **Cough reflex** | Weak/absent | Normal | | **Pitch control** | Lost | Impaired | **Key Point:** RLN injury causes ipsilateral vocal cord paralysis in paramedian position → breathy hoarseness. SLN injury affects cricothyroid muscle innervation → loss of pitch control and vocal projection without hoarseness. ### Anatomical Basis **RLN (Inferior laryngeal nerve):** - Innervates all intrinsic laryngeal muscles except cricothyroid - Injury → vocal cord immobility in paramedian position - Results in breathy, weak voice **SLN (External branch):** - Innervates cricothyroid muscle (tensor of vocal cords) - Injury → loss of vocal cord tension - Results in vocal fatigue and loss of pitch projection **Clinical Pearl:** A patient with RLN injury complains of "my voice sounds breathy and weak." A patient with SLN injury complains of "I cannot sing high notes and my voice gets tired." This distinction is the gold standard for immediate postoperative differentiation. **High-Yield:** Bilateral RLN injury → stridor and potential airway emergency. SLN injury is often missed because voice quality may seem relatively preserved initially. **Tip:** In the exam, look for "breathy hoarseness" (RLN) vs "vocal fatigue/loss of pitch" (SLN) as the key discriminator. 
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