Table 2.
Summary of clinical studies on intradermal and intramuscular botulinum toxin injections for the treatment of AGA
| Study | Design | Injections | Measurements | Outcomes | Safety | Jadad score |
|---|---|---|---|---|---|---|
| Freund et al. [18] | Prospective cohort, open-label pilot study Male AGA subjects (n = 50) recruited in Canada, aged 19–57 years, Norwood-Hamilton class II to IV with no hair loss treatments in the last 12 months 60-week duration, 12-week run-in period |
150 units of botulinum toxin type A injected into frontalis, temporalis, periauricular, and occipitalis muscles Equally divided doses over 30 injection sites Two sessions performed |
Primary outcome: changes to hair count in a fixed 2-cm area Secondary outcomes: subjective efficacy questionnaire and collection of shed hairs from subjects' pillows |
40 subjects completed the study Response rate: 75% Mean hair counts increased by 18% between baseline and 48 weeks Mean number of hairs shed decreased by 39% at week 28 No statistically significant correlation between reduction in hair shedding and increase in hair count |
No AEs reported | 0 |
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| Singh et al. [19] | Prospective cohort study Male AGA subjects (n = 10) recruited in India, aged 22–42 years, Norwood-Hamilton II to IV with no hair loss treatments in the last 6 months 24-week duration | 150 units of botulinum toxin type A injected into frontalis, temporalis, periauricular, and occipitalis muscles Equally divided doses over 30 injection sites | Primary outcomes: photographic assessment, graded on a scale of 0–3 (0 = poor, 1 = fair, 2 = good, 3 = excellent) by subjects and observers | 80% (n = 8) of subjects were graded as having an excellent response after 24 weeks 10% (n = 1) of subjects were graded as having a poor response after 24 weeks 10% (n = 1) of subjects were graded as having a fair response after 24 weeks As per self-assessment, 70% (n = 7) of subjects graded themselves as having an excellent response after 24 weeks As per self-assessment, 20% (n = 2) of subjects graded themselves as having a fair response after 24 weeks As per self-assessment, 10% (n = 1) of subjects graded themselves as having a poor response after 24 weeks |
No AEs reported | 1 |
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| Zhang et al. [20] | Prospective cohort study Male AGA subjects (n = 24) recruited in China, aged 30–45 years with an unreported hair loss treatment history Clinical evaluations performed at 3 and 6 months | 50 units of botulinum toxin type A injected into frontalis, temporalis, periauricular, and occipitalis muscles Equally divided doses over 30 injection sites One session | Primary outcomes: scalp sebum content (as assessed by Derma-Expert MC760) and hair counts | After 6 months, 11 subjects exhibited increases in hair counts > 10%, 8 demonstrated minimal improvement, and 5 showed no response to treatment, corresponding to a response rate of 79.1% In 19 subjects, sebum secretion decreased at the 3-month mark, and then normalized by 6 months |
No AEs reported | 1 |
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| Shon et al. [21] | Prospective cohort study Male AGA subjects (n = 18) recruited in South Korea, mean age of 49 years, enrolled based on basic and specific classification with an unreported hair loss treatment history | 30 units of botulinum toxin type A injected intradermally into 20 different sites on the balding scalp every 4 weeks for 24 weeks | Primary outcomes: mean change in hair counts per cm2 and change in TGF-β1 expression in cultured DPCs | Mean hair counts increased by 5.1 % at 24 weeks DHT upregulated TGF-β1 expression in DPCs in 96 h, whereas botulinum toxin type A downregulated TGF-β1 expression | No AEs or changes in laboratory parameters reported | 0 |
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| Zhou et al. [22] | Randomized trial Two treatment groups: botulinum toxin type A injections and botulinum toxin type A + finasteride Male AGA subjects (n = 63) recruited in China with no prior treatment history of drugs that may interfere with botulinum toxin within the last 6 months 12-month duration Randomized into either group by a simple randomization grouping method botulinum toxin type A only n = 30 Mean age: 38.47 years Mean disease duration: 8.85 years Norwood-Hamilton II vertex: 30% (n = 9) Norwood-Hamilton III: 43.3% (n = 13) Norwood-Hamilton IV: 26.7% (n = 8) Botulinum toxin type A + finasteride n= 33 Mean age: 40.06 years Mean disease duration: 7.83 years Norwood-Hamilton II vertex: 45.4% (n = 7) Norwood-Hamilton III: 33.3% (n = 15) Norwood-Hamilton IV: 26.7% (n = 11) |
100 units of botulinum toxin type A injected into frontalis, temporalis, periauricular, and occipitalis muscles 30 injection sites, 1.5–2 cm apart Injections performed every 3 months, 4 treatments in total | Primary treatment outcomes: mean change in hair count over a 2-cm2 area, independent photographic assessment rated on a 4-point scale with 0 defined as poor, 1 as fair, 2 as good, and 3 as excellent, effective rate calculated by (good + excellent)/(poor + fair + good + excellent) ×100% Additional outcomes: self-assessment questionnaire on hair loss, dandruff, and scalp oil secretion |
Mean hair count change in botulinum toxin type A only group: 20.9% Mean hair count change in botulinum toxin type A + finasteride group: 31.3% Response rate in botulinum toxin type A only group: 73.3% Response rate in botulinum toxin type A + finasteride group: 84.8% 16 and 23 subjects in the botulinum toxin type A only group and botulinum toxin type A + finasteride group, respectively, reported moderate and marked improvement in symptoms of scalp oil secretion, pruritus, and dandruff 23 and 27 subjects in the botulinum toxin type A only group and botulinum toxin type A + finasteride group, respectively, reported moderate and marked reduction in hair loss as compared with before treatment |
No severe AEs reported One subject in botulinum toxin type A only group developed headache Injection site events (i.e., pain, erythema, or edema) were reported in 2 subjects in the botulinum toxin type A only group and 1 subject in the botulinum toxin type A + finasteride group Slight breathlessness and nausea associated with botulinum toxin type A injection was reported by 1 subject in the botulinum toxin type A + finasteride group |
3 |
Details include study groups, designs, injection methodologies, measurement end points, outcomes, AEs, and quality scores. AGA, androgenic alopecia; TGB-β1, transforming growth factor beta 1; DPCs, dermal papillae cells; DHT, dihydrotestosterone; AEs, adverse events.