J Korean Soc Laryngol Phoniatr Logoped.  2025 Aug;36(2):75-78. 10.22469/jkslp.2025.36.2.75.

Sternothyroid Muscle Dystonia as an Unusual Cause of Dysphonia: A Case Report and Review of Diagnostic and Therapeutic Strategies

• Kang YJ
• Kwon TK

• KMID: 2571290
• DOI: http://doi.org/10.22469/jkslp.2025.36.2.75

Abstract

The causes of dysphonia are diverse. When bilateral vocal fold motion is normal and there are no mucosal lesions, conditions such as muscle tension dysphonia (MTD) and neurologic disorders should be considered in the differential diagnosis. To our knowledge, no prior reports have described sternothyroid muscle dystonia as a cause of dysphonia. We present a case of a 58-yearold female diagnosed with sternothyroid muscle dystonia. Her voice changes developed without any notable medical or social history. Laryngoscopic examination revealed no mucosal abnormalities or vocal fold immobility, except for vocal fold bowing, and her voice was unusually low in pitch for her age and sex. Notably, a downward movement of the larynx during phonation was observed without corresponding movement of the hyoid bone. Initial treatments—including voice therapy to rule out MTD and injection laryngoplasty for vocal fold atrophy—were unsuccessful. Suspecting sternothyroid muscle dystonia, botulinum toxin A was injected into the muscle, resulting in voice improvement. With repeated injections, followed by surgical division of the muscle, further subjective voice improvement was observed. Focal muscle dystonia affecting the voice is rare, and dystonia of the sternothyroid muscle has not previously been described. This case suggests that sternothyroid muscle dystonia may be an underrecognized cause of dysphonia. Furthermore, it may be effectively treated with botulinum toxin A injections and surgical intervention in patients whose larynx descends during phonation. We aim to introduce sternothyroid muscle dystonia as a novel etiology of dysphonia and describe its potential treatment options.

Keyword

Dysphonia; Dystonia; Botulinum toxins; Electromyography; Sternothyroid muscle