## Most Common Cause of Bilateral Vocal Cord Paralysis **Key Point:** Thyroid pathology (surgery, malignancy, or compression) is the most common cause of bilateral vocal cord paralysis, accounting for 30–40% of cases in most series. ### Mechanism of Injury The recurrent laryngeal nerve (RLN) has a long course in the neck, making it vulnerable to: - Direct injury during thyroid surgery (most common iatrogenic cause) - Compression by thyroid malignancy or goiter - Infiltration by metastatic disease ### Clinical Context in This Case The patient has a history of thyroid cancer, which significantly increases the likelihood of bilateral RLN involvement through: 1. Surgical trauma during thyroidectomy 2. Tumor infiltration of both RLNs 3. Lymph node metastases compressing the nerves ### Differential Causes of Bilateral VCP | Cause | Frequency | Key Features | |-------|-----------|-------------| | **Thyroid pathology** | 30–40% | History of surgery or malignancy; paramedian position | | Idiopathic | 20–30% | Diagnosis of exclusion; no identifiable cause | | Brainstem lesion | 10–15% | Central cause; often with other neurologic signs | | Poliomyelitis | <5% | Rare in vaccinated populations; motor neuron disease | | Intubation trauma | 5–10% | History of prolonged intubation or difficult airway | **High-Yield:** In a patient with thyroid cancer and bilateral VCP, assume thyroid-related injury until proven otherwise. **Clinical Pearl:** Bilateral paramedian VCP is the classic presentation of RLN injury; the cords are pulled medially by the cricothyroid muscles (innervated by the external branch of the superior laryngeal nerve, which is spared).
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