Question

A singer presents with problem in high pitch. On examination bowing of one side vocal cord. Which of the following muscle is affected?

• A. Posterior cricoarytenoid
• B. Lateral cricoarytenoid
• C. Cricothyroid
• D. Thyroarytenoid

Hint:

High pitch needs a taut, lengthened cord. Which intrinsic laryngeal muscle is the tensor (supplied by the external laryngeal nerve)?

Answer 1

The Correct Option is C

Step 1: Link the symptom to vocal-cord function. Producing a HIGH-PITCHED voice requires the vocal cords to be lengthened and tensed (stretched taut). The muscle responsible for tensing/elongating the vocal cords is the cricothyroid.
Step 2: Cricothyroid action and nerve. The cricothyroid tilts the thyroid cartilage forward/down on the cricoid, which stretches and tenses the vocal folds, raising pitch. It is the ONLY intrinsic laryngeal muscle supplied by the external branch of the superior laryngeal nerve (all other intrinsic muscles are supplied by the recurrent laryngeal nerve).
Step 3: Interpret the sign. When the cricothyroid is paralysed/weak, the affected cord cannot be tensed and elongated, so it loses tone and appears bowed (wavy/loss of straight tense edge), and the patient - especially a professional singer who needs precise high notes - complains of inability to reach high pitch and easy vocal fatigue. This is the classic presentation of cricothyroid / external superior laryngeal nerve palsy.
Step 4: Why option C is correct and the others wrong. (C) Cricothyroid tenses the cord for high pitch; its weakness causes bowing and high-pitch loss - correct. (A) Posterior cricoarytenoid is the only ABDUCTOR (opens the glottis for breathing); its palsy affects abduction/airway, not pitch tensing. (B) Lateral cricoarytenoid ADDUCTS the cords (closes glottis); not the pitch-raising tensor. (D) Thyroarytenoid (vocalis) shortens/relaxes and fine-tunes the cord and is a weak adductor; it does not produce the high-pitch tensing that the cricothyroid provides.
Final answer: C. Cricothyroid.