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Journal of Voice, Vol. 29, No. 3, 2015

BTX treatment for more than three visits. This study found that patients on average reached their stable dosing regimen after 1.34 months. They did not find any statistically significant dose variability, but they found the following trends, namely increased average dosage for patients who were on their 15th treatment or later, decreased average time interval between treatments over time, and decreased dosage over time in pa tients beginning treatment in their sixth and seventh decades. An earlier study had found that patients who started with lower dosage of at most 1.5 units per side had stable dosing, whereas those who started at higher doses of 2.5 units per side had a nonsignificant trend toward a lower dose, indicating that this starting dose may have been too high. 3 However, this study was limited by its small number of patients (13) who met the inclusion criterion of undergoing a minimum of six injections. In contrast, our study has the largest patient sample to date of any research addressing this topic. This allows us to use regression analysis to more effectively determine the rela tionship between the variables at hand than by simple corre lation. One potential weakness of this study is the use of a nonvalidated perceptual voice measure to determine patient satisfaction after BTX treatment. Our patient population dates back to 1990, when validated instruments such as Voice Handicap Index or Voice-Related Quality of Life were not yet available. Second, Braden et al 14 demonstrated that there was poor correlation between self-reported instruments and validated clinician tools such as Consensus Auditory Perceptual Evaluation of Voice, confirming that there is still no consensus approach to evaluating voice outcomes in ADSD patients. Our findings should allow for better patient counseling regarding expectations for their long-term treatment. Patients are often concerned that a BTX dose that gives them good voice quality on one occasion may not work the next time they go for treatment, or that their dose will gradually stop providing them with an improved voice over time. This study lends evidence to the idea that once patients find a stable dose that gives them good voice quality, they are likely to stay at that dose. This may help alleviate patients’ anxiety about seeing consistent benefits because as our results show, it is likely that this dose will remain stable over time.

TABLE 2. Demographic Summary by Gender

N (%)/Mean (SD)

N (%)/mean (SD)

Demographics

Female

Male

N (%)

165 (78.2) 56.9 (14.9) 10.5 (10.4)

46 (21.8)

Age

50.3 (13.0) 12.2 (10.4)

Number of injections

Number of dosage changes 1.7 (2.2)

2.4 (3.6)

Abbreviation: SD, standard deviation.

For example, Birkent et al 11 showed that the mean dose required for effective treatment decreased slightly over time, with a statistically significant decrease of 0.35 units noted at the 13th injection. They found that the mean duration of good effect and treatment intervals did not change. Interest ingly, the same group also published findings that age and gender had no statistical effect on BTX dose amount or dose efficacy. 12 Our group demonstrated in 1998 that self-reported voice out comes of older SD patients were poorer than in younger patients after BTX treatment. 6 This was a retrospective review of 68 SD patients and found that voice outcome was significantly corre lated with age, severity of SD symptoms, and presence of asso ciated movement disorders, so the age findings may have been confounded by worse overall disease severity in the older group. Patients older than 65 years were more likely to continue experiencing mild-to-moderate SD symptoms after injection than younger patients. Men were found to respond on average 6 weeks longer than women, and patients undergoing bilateral injections responded on average 6.5 weeks longer than those having unilateral injections. These findings were corroborated later by an article that grouped patients into decades by age and controlled for factors including disease severity and amount of time postdiagnosis. 7 That study found that patients older than 70 years experienced significantly less improvement in their voice quality after BTX treatment. Chinosornvatana et al 13 published an abstract in 2011 retro spectively reviewing 182 ADSD patients, 87 of whom received

TABLE 3. Logistic Regression With General Estimating Equation

95% Confidence Intervals

Parameters

Odds Ratios*

Lower Limit

Upper Limit

Number of beneficial injections

0.964 0.988

0.947 0.975

0.981 1.002

Age

Smoking status

Never vs current Former vs current

0.995 1.063

0.544 0.543

1.821 2.079

* Modeling outcome: dosage change ¼ ‘‘Yes.’’