A 58-year-old man presents with progressive hoarseness and dysphagia for 3 weeks. On laryngoscopy, the left vocal cord is found to be in the paramedian position with reduced mobility. Which investigation is most appropriate to identify the underlying etiology?

Explanation

## Investigation of Choice for Vocal Cord Paralysis Etiology ### Clinical Context The patient presents with unilateral vocal cord paralysis (UVCP) in the paramedian position. While laryngoscopy confirms the paralysis, it does NOT identify the cause. The most common etiologies include: - Malignancy (lung, thyroid, esophageal) - Thyroid surgery complications - Mediastinal pathology - Idiopathic (20–30% of cases) ### Why Contrast-Enhanced CT Chest and Neck? **Key Point:** CT imaging is the investigation of choice for identifying structural causes of vocal cord paralysis along the entire course of the recurrent laryngeal nerve (RLN) and vagus nerve. **High-Yield:** The recurrent laryngeal nerve has a long course: - Left RLN: loops under the aortic arch (vulnerable to mediastinal/cardiac pathology) - Right RLN: loops under the subclavian artery - Both nerves ascend through the tracheoesophageal groove (vulnerable to thyroid, esophageal, and tracheal pathology) Contrast-enhanced CT allows visualization of: 1. Lung masses (most common malignant cause) 2. Thyroid enlargement or nodules 3. Mediastinal masses 4. Esophageal pathology 5. Post-surgical changes **Clinical Pearl:** In any patient with new-onset unilateral vocal cord paralysis, malignancy must be excluded first. CT chest is mandatory before attributing the paralysis to "idiopathic" causes. ### Table: Investigation Comparison in Vocal Cord Paralysis | Investigation | Purpose | Identifies Cause? | Assesses Function? | | --- | --- | --- | --- | | **CT chest/neck** | Structural lesions along RLN/vagus course | **Yes** | No | | Videostroboscopy | Vocal cord vibratory characteristics | No | Yes | | EMG of laryngeal muscles | Denervation pattern, prognosis | No | Partially | | Flexible laryngoscopy | Confirms paralysis, assesses position | No | Partially | ### Diagnostic Algorithm ```mermaid flowchart TD A[Vocal Cord Paralysis Suspected]:::outcome --> B{Confirmed on Laryngoscopy?}:::decision B -->|Yes| C[Obtain CT Chest + Neck with Contrast]:::action C --> D{Lesion Found?}:::decision D -->|Yes - Malignancy| E[Staging + Oncology referral]:::action D -->|Yes - Thyroid| F[Thyroid ultrasound + FNA if nodule]:::action D -->|No| G[Idiopathic VCP]:::outcome G --> H[Videostroboscopy for prognosis]:::action H --> I[EMG if recovery assessment needed]:::action ``` **Key Point:** Videostroboscopy and EMG are functional/prognostic tests, not diagnostic tests for etiology. They come AFTER structural imaging has excluded serious pathology. [cite:Scott-Brown's Otolaryngology 8e Ch 35]