Retroform Cervical Dystonia: Target Muscle Selection and Efficacy of Botulinum Toxin Injection

Abstract

Introduction: Retroform cervical dystonia (RCD), which includes retrocaput and retrocollis, is a rare form of cervical dystonia. Few reports have been published on RCD. The present study aimed to characterize the target muscles involved in RCD and the efficacy of botulinum toxin type A (BTX-A) injection.

Methods: Patients with consecutive cervical dystonia with RCD as the most problematic feature were retrospectively analyzed over a 10-year period. Target muscles were screened and confirmed based on clinical evaluation, single-photon emission computed tomography, and electromyography. In addition, efficacy and adverse events following BTX-A injection in patients with RCD were evaluated.

Results: A total of 34 patients with RCD were included, 18 of whom presented with retrocaput and 16 with retrocollis. The most frequently injected muscles in RCD were splenius capitis (SPCa, 97.1%) and semispinalis capitis (SSCa, 97.1%), followed by levator scapulae (LS, 50.0%), rectus capitis posterior major (RCPM, 47.1%), trapezius (TPZ, 41.2%), and sternocleidomastoid muscle (SCM, 41.2%). Besides cervical muscles, the erector spinae was also injected in 17.6% of patients. Most muscles were predominantly bilaterally injected. The injection schemes of retrocaput and retrocollis were similar, possibly because in patients with retrocollis, retrocaput was often combined. BTX-A injection achieved a satisfactory therapeutic effect in RCD, with an average symptom relief rate of 69.0 ± 16.7%. Mild dysphagia (17.6%) and posterior cervical muscle weakness (17.6%) were the most common adverse events.

Conclusion: SPCa, SSCa, LS, RCPM, LS, and SCM were commonly and often bilaterally injected in RCD. Patients with RCD could achieve satisfactory symptom relief after BTX-A injection.

Keywords: botulinum toxin; cervical dystonia; retrocaput; retrocollis; single-photon emission computed tomography.

Figure 1

Representative pictures of patients with RCD. (A) Retrocaput before BTX-A injection; (B) retrocaput after BTX-A injection; (C) retrocollis before BTX-A injection; and (D) retrocollis after BTX-A injection.

Figure 2

Representative SPECT/CT images of different activated cervical muscles in patients with RCD. (A) Bilateral activation of splenius capitis (SPCa) indicated by the white arrows; (B) bilateral activation of semispinalis capitis (SSCa) indicated by the white arrows; (C) bilateral activation of sternocleidomastoid muscle (SCM) indicated by the white arrows; (D) bilateral activation of trapezius (TPZ) indicated by the white arrows; (I) bilateral activation of levator scapulae (LS) indicated by the white arrows; (J) bilateral activation of rectus capitis posterior major (RCPM) indicated by the white arrows; and (K) bilateral activation of erector spinae (ES) indicated by the white arrows. To demonstrate the anatomy of cervical muscles more clearly, we put the CT images of the same level below each SPECT image and outlined the boundaries of related muscles. (E–H) are CT images of (A–D) respectively, and (L–N) are CT images of (I–K) respectively. OCI, obliquus capitis inferior; SSCe, semispinalis cervicis.