A 58-year-old man presents with progressive hoarseness and dyspnea on exertion for 3 weeks. He underwent thyroid surgery 4 weeks ago for multinodular goiter. On laryngoscopy, the left vocal cord is seen in the paramedian position and does not abduct during inspiration. The right vocal cord moves normally. What is the most likely diagnosis?

Explanation

## Clinical Diagnosis: Left Recurrent Laryngeal Nerve (RLN) Injury ### Anatomical Basis The recurrent laryngeal nerve innervates all intrinsic laryngeal muscles except the cricothyroid (which is innervated by the superior laryngeal nerve). RLN injury results in: - Loss of abductor function (posterior cricoarytenoid muscle) - Preservation of adductor function (lateral cricoarytenoid, interarytenoid muscles) - Vocal cord assumes a **paramedian position** (midway between abduction and adduction) ### Clinical Presentation **Key Point:** The paramedian position is pathognomonic for RLN injury because: 1. The cord cannot abduct (no posterior cricoarytenoid activity) 2. The cord is pulled slightly medially by residual cricothyroid activity (SLN intact) 3. Adductors are weakened but not completely paralyzed ### Why This Case is RLN Injury - **Timing:** Injury occurred during thyroid surgery (RLN runs in the tracheoesophageal groove) - **Unilateral presentation:** Left cord affected; right cord normal - **Position:** Paramedian (classic RLN sign) - **Abduction loss:** Cord does not move during inspiration - **Adduction preserved:** Cord can still be adducted by remaining adductors ### Differential Features | Feature | RLN Injury | SLN Injury | Vagus Nerve Injury | |---------|-----------|-----------|-------------------| | Cord position | Paramedian | Lateral/abducted | Paramedian | | Abduction | Lost | Preserved | Lost | | Voice quality | Breathy, weak | High-pitched, fatigable | Breathy + hoarse | | Aspiration risk | Moderate | Minimal | High | | Affected muscles | All intrinsic (except CT) | Cricothyroid only | All laryngeal | **Clinical Pearl:** Post-thyroid surgery RLN injury is the most common iatrogenic laryngeal nerve injury, occurring in 0.5–2% of cases. The nerve is at risk during dissection of the superior pole and during ligation of inferior thyroid vessels. **High-Yield:** A paramedian vocal cord position = RLN injury until proven otherwise.