A 52-year-old male presents with progressive hoarseness and dysphagia for 3 weeks. On examination, the left vocal cord is found to be in a paramedian position. Which investigation is most appropriate to determine the etiology of this vocal cord paralysis?

Explanation

## Investigation of Choice for Vocal Cord Paralysis Etiology **Key Point:** When vocal cord paralysis is clinically diagnosed, imaging of the entire course of the recurrent laryngeal nerve (RLN) and vagus nerve is mandatory to identify the underlying cause. ### Why Contrast-Enhanced CT Chest and Neck? Contrast-enhanced CT is the gold standard for identifying structural causes of vocal cord paralysis because it: 1. **Visualizes the entire RLN pathway** — from the brainstem through the neck, thorax, and mediastinum to the larynx 2. **Detects common etiologies:** - Thyroid enlargement or malignancy - Lung apex tumors (Pancoast tumor) - Mediastinal masses - Aortic aneurysm - Skull base lesions 3. **Provides anatomical detail** superior to other modalities for soft tissue and bony structures **High-Yield:** In India, thyroid pathology (benign goiter, thyroid cancer) and lung malignancy are the most common causes of RLN paralysis. CT will detect both. ### Differential Approach to Investigations | Investigation | Purpose | Limitations | |---|---|---| | **CT chest/neck** | Structural imaging of RLN course | Gold standard for etiology | | Laryngoscopy | Confirms cord position & mobility | Does NOT identify cause | | EMG | Assesses nerve/muscle integrity | Functional test; no anatomical diagnosis | | TFTs | Screens thyroid dysfunction | Thyroid disease may not cause paralysis | **Clinical Pearl:** Laryngoscopy confirms the diagnosis (cord immobility) but does NOT reveal why the nerve is damaged. You must image the nerve pathway. **Mnemonic — RLN Paralysis Causes (CHAMP):** - **C**ardiac (aortic aneurysm, cardiac surgery) - **H**ead/Neck (skull base, thyroid) - **A**irway/mediastinal (lung cancer, Pancoast) - **M**ediastinal masses - **P**ost-surgical (thyroid, cardiac, esophageal surgery) ### Typical Workup Algorithm ```mermaid flowchart TD A[Vocal cord paralysis on laryngoscopy]:::outcome --> B[Contrast-enhanced CT chest/neck]:::action B --> C{Etiology found?}:::decision C -->|Yes: Thyroid/lung/mediastinal mass| D[Treat underlying cause]:::action C -->|No: Idiopathic| E[Consider EMG for prognosis]:::action E --> F[Supportive care/voice therapy]:::action ``` **Tip:** Always order **bilateral** imaging (not just the affected side) because contralateral subclinical involvement may be present, especially in malignancy.