Determinants of Therapeutic Success: Patient and Procedural Factors in Injection-Based Treatment of Myofascial Pelvic Pain

INTRODUCTION: Despite recent expert consensus guidelines for high-tone pelvic floor dysfunction management, the evidence base for second-line treatments in patients who fail to respond to conservative measures including behavioral modifications and pelvic floor physical therapy remains insufficient. OBJECTIVE: To describe patient characteristics and injection techniques associated with trigger point injection (TPI) and botulinum toxin injection (BTX-A) success in patients with myofascial pelvic pain (MPP). METHODS: This retrospective chart review was conducted at an academic minimally invasive gynecologic surgery clinic from January 2021 to December 2023. Adult women diagnosed with MPP who received TPI (n=66) or BTX-A injections (n=17) were identified using ICD-9, ICD-10, and CPT codes. Treatment “success” was defined as symptom resolution or continued treatment maintenance, whereas treatment “failure” was defined as progression to alternative therapies due to inadequate symptom improvement or documented patient-reported lack of benefit. Variables included demographic data, presence of chronic overlapping pain conditions (COPCs) (endometriosis, vulvodynia, fibromyalgia, interstitial cystitis/bladder pain syndrome, irritable bowel syndrome, chronic low back pain, tension-type headache or migraine headache, myalgic encephalitis/chronic fatigue syndrome or temporomandibular joint disorder), comorbid pelvic floor symptoms (lower urinary tract, bowel or sexual dysfunction symptoms), and injection techniques. Statistical comparisons utilized t-tests for continuous variables and Pearson’s chi-square statistic or Fisher’s exact test for categorical variables. RESULTS: TPIs demonstrated higher success rates compared to botulinum toxin A injections, with 83% of TPI patients (55/66) reporting treatment success versus 53% of BTX-A patients (9/17). The majority of TPIs targeted the levator ani muscles (n=54, 81.8%), with fewer administered to the superficial transverse perineal muscles (n=7, 10.6%). Concomitant pudendal blocks were performed in 14 patients (21.2%). The mean volume of 0.25% bupivacaine used was 10.2 mL (SD 3.9). Triamcinolone was added to injections of 45 patients, with a standardized dose of 40 mg in 44 cases (97.8%). BTX-A injections were predominately administered as 100 units (n=11, 64%), given bilaterally (n=13, 76.5%) primarily targeting the levator ani (n=16, 94.1%). No significant associations were identified between TPI success and demographics (age, race, ethnicity, employment status, or insurance type), individual COPCs or having any COPC, comorbid pelvic floor symptoms, or injection techniques (Table 1). For BTX-A injections, eight patients had previously failed TPI, suggesting a more treatment-refractory cohort. Patients with BTX-A success were significantly older (mean age 56.3 years vs 40.1 years, p=0.03) and had higher Charlson comorbidity indices (median 3.0 vs 0.5, p=0.024). No other demographic, clinical, or technical factors were associated with BTX-A treatment success (Table 2). CONCLUSIONS: Both trigger point injections and botulinum toxin A injections demonstrated favorable outcomes for treating pelvic floor myalgia. While no patient or technical factors predicted TPI treatment success, BTX-A outcomes were significantly associated with patient age and comorbidity burden, with older patients and those with higher Charlson comorbidity indices more likely to experience treatment benefit. These findings suggest that patient selection criteria may be more relevant for BTX-A than TPI when treating myofascial pelvic pain.Table 1Table 2