A 68-year-old man with a 20-year history of hypertension presents to the ENT clinic with progressive hoarseness and weak voice for 3 months. He denies dysphagia or dyspnea at rest. On flexible laryngoscopy, the left vocal cord is seen in a paramedian position with absent abduction during inspiration. The right vocal cord moves normally. CT chest is unremarkable. Which of the following is the most likely diagnosis?

Explanation

## Clinical Presentation Analysis **Key Point:** The paramedian position of the vocal cord with absent abduction during inspiration is pathognomonic for recurrent laryngeal nerve (RLN) palsy. ### Anatomy of Vocal Cord Innervation | Nerve | Motor Supply | Function | Cord Position in Palsy | |-------|--------------|----------|------------------------| | Recurrent Laryngeal Nerve (RLN) | All intrinsic muscles except cricothyroid | Abduction (PCA), adduction (LCA, IA, TA) | Paramedian (cadaveric position) | | Superior Laryngeal Nerve (SLN) | Cricothyroid muscle only | Tension and pitch control | Lateral position, shortened | | Vagus nerve (CN X) | All above combined | Complete laryngeal function | Lateral (if bilateral) | ### Why This Is RLN Palsy 1. **Paramedian position** — The RLN innervates the posterior cricoarytenoid (the only abductor). Loss of RLN function leaves the adductors unopposed, pulling the cord to midline. 2. **Absent abduction during inspiration** — PCA is paralyzed; the cord cannot move laterally. 3. **Hoarseness** — Loss of adductor function causes incomplete glottic closure. 4. **Unilateral presentation** — Only the left cord is affected; right cord is normal. **Clinical Pearl:** In RLN palsy, the cord typically rests 2–3 mm from the midline (paramedian), NOT at the midline itself. This is because some passive elastic recoil and gravity allow slight lateral drift. ### Etiology in This Patient Common causes of unilateral RLN palsy: - Malignancy (lung, thyroid, mediastinal) — most common in adults - Thyroid surgery - Cardiac surgery - Idiopathic (~30% of cases) - Aortic aneurysm - Tuberculosis Although CT chest is unremarkable, further imaging (chest X-ray, thyroid ultrasound) and thyroid function tests are warranted. **High-Yield:** Idiopathic RLN palsy often recovers spontaneously within 3–6 months. If no recovery by 6 months, consider malignancy or structural lesion.