(SD)
Spasmodic dysphonia (SD) is a rare, chronic voice disorder characterized by involuntary spasms of the laryngeal muscles, resulting in a strained, strangled, or breathy voice16. While SD itself is a distinct neurological disorder, research shows that other vocal and movement disorders frequently co-exist in these patients.

Common Co-existing Vocal and Movement Disorders
• Vocal Tremor:
Vocal tremor is one of the most frequently reported coexisting conditions, found in approximately 29% of SD cases28. It may occur independently or alongside SD, further complicating the voice presentation and sometimes making diagnosis more challenging8.
• Muscle Tension Dysphonia:
Muscle tension dysphonia, characterized by excessive muscular effort during phonation, can co-occur with SD and contribute to the overall strain and abnormal voice quality8.
• Glottic Incompetence:
Some patients with SD also exhibit glottic incompetence, which can result in additional vocal strain and incomplete vocal fold closure during speech8.
• Sulcus Vocalis:
A significant association has been observed between SD patients—especially those with an abductor component (abductor SD and mixed SD)—and the presence of sulcus vocalis, a structural abnormality of the vocal fold7.
• Other Neurological Movement Disorders:
Studies reveal a high prevalence of other movement disorders among SD patients, including orofacial dystonia (50%), essential tremor (50%), and spastic paraparesis (12%)5. These findings suggest a broader neurological vulnerability in SD, often classified as a focal laryngeal dystonia5.

Clinical Implications
The coexistence of these disorders can complicate both the diagnosis and management of SD. For example, the presence of vocal tremor or muscle tension dysphonia may affect the response to standard treatments such as botulinum toxin injections, and may necessitate a more comprehensive, multidisciplinary approach to therapy8.

Conclusion
Patients with spasmodic dysphonia frequently present with additional vocal and neurological disorders, most notably vocal tremor, muscle tension dysphonia, glottic incompetence, sulcus vocalis, and other movement disorders2578. Recognizing and addressing these coexisting conditions is essential for optimizing diagnosis, treatment, and patient outcomes.
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