The role of platelet‐rich plasma in androgenetic alopecia: A systematic review

Androgenetic alopecia (AGA), also referred to as male or female pattern hair loss, is the commonest cause of chronic hair loss and affects up to 80% of men by the age of 70. Despite a high prevalence, there are few approved therapies, which show minimal efficacy.


| INTRODUC TI ON
Androgenetic alopecia (AGA), also referred to as male or female pattern hair loss, is the commonest cause of chronic hair loss and affects up to 80% of men and 40% of women by the age of 70. 1,2[3] Despite a high prevalence, there are few approved therapies, which show minimal efficacy. 1,4,5Current National Institute of Clinical Excellence (NICE) and Food and Drug Administrationapproved (FDA) medical treatments include finasteride and minoxidil, 4,5 though these only slow hair loss, and are associated with considerable side effects, including unwanted non-scalp hair, sexual dysfunction, potential effects on fetal development and local skin reactions. 5atelet-rich plasma (PrP), an autologous blood product containing a high concentration of platelets (150 000-350 000/L), has been proposed as a novel treatment for AGA, with a lower side effect profile. 2,3,6The intradermal application of concentrated growth factors to AGA-affected areas has been shown to enhance tissue regeneration and wound healing. 6It is also less invasive and cheaper than surgical options, such as hair transplants. 4netheless, it is not currently licensed for use in AGA by the FDA or NICE. 4,5evious systematic reviews investigating PrP use in AGA have been limited by heterogenous study populations and treatment regimens, as well as low-powered, included studies. 3,7This systematic review aims to evaluate the efficacy of PrP in the treatment of AGA in male patients due to its high prevalence in this cohort.

| Protocol and registration
This review was conducted in adherence to the Preferred Reporting Items for Systematic Reviews (PRISMA) statement (Appendix S1). 8 The protocol was registered prospectively with the Prospective Register of Systematic Reviews (PROSPERO; CRD 42021265858). 9Combinations of Medical Subject Headings (MeSH) terms and free text terms were used in addition to other operators such as Boolean logical operators.An example of an EMBASE (Ovid SP) strategy was adopted for other databases (Appendix S2).

| Inclusion criteria
Eligible searches were limited to prospective cohort studies and randomized controlled trials (RCTs) involving male adults with AGA undergoing treatment with PrP or placebo.

| Exclusion criteria
Studies enrolling individuals with non-androgenetic alopecia were excluded.In addition, articles such as abstracts, presentations, editorial letters, commentaries, surveys, reviews, case reports, and case series were excluded along with studies involving nonhuman subjects.

| Study screening
Studies from the database searches were entered into the EndNote library (Clarivate Analytics, Philadelphia, USA).Two investigators independently screened the titles and abstracts, and then the fulltexts of potentially eligible papers, using the prespecified criteria.
Any discrepancies were resolved by discussion with a third author.
Studies investigating PrP use in both male and female patients, without reporting stratified results, were contacted to provide a breakdown of their results according to gender.Any studies where a breakdown of male and female patient outcomes could be distinguished were included.

| Data extraction
Data were extracted using a standardized data extraction form created for this review (Appendix S3).Authors were contacted twice to provide any missing data for the outcomes investigated.

| Study outcomes
Primary outcomes included hair density, hair growth, hair count (hair pull test), hair diameter, hair mass index, anagen hair, anagen-telogen ratio, terminal hair density, the epidermal thickness of hair follicle, number of Ki67+ basal cell proliferation, number of small blood vessels around hair follicles, and number of basal keratinocytes.
Secondary outcomes included the number of clinic visits and sessions, and patient-reported outcomes.

| Methodological quality assessment
Two investigators assessed the methodological quality and risk of bias of included studies, with any discrepancies resolved by a third author.The Grading of Recommendations Assessment, Development, and Evaluation (GRADE) was used to assess the methodological quality of studies as: high, moderate, low, or very low. 10 The Cochrane Risk of Bias Assessment (RoB2) was used for RCTs, comprising five domains, which produce an overall score classified as low risk, some concerns, or high risk. 11The ROBINS-I tool was used for prospective cohort studies consisting of seven domains, which produce an overall score classified as: low, moderate, serious, or critical risk. 12

| RE SULTS
The search identified 400 papers after removal of duplicates, of which 42 were considered eligible for full-text screening (See Figure 1).Ultimately, 9 papers met the inclusion criteria, which assessed PrP treatment compared with placebo in 291 male patients with AGA.There were 8 single-center RCTs and 1 singlecenter cohort study (See Table 1).Two studies were conducted in India.
All the studies classified AGA severity using the Hamilton and Norwood scale and included patients with different AGA severities in their cohorts (See Table 1).Males of different ages were included in the studies.Different means of preparing PrP were used, and the amount of injected PrP ranged from 1 to 2 milliliters.Papers used varying treatment protocols.(See Table 2).

| Hair density
4][15][16][17] Gentile et al. also reported a significant increase in hair follicular bulge cells and the number of small blood vessels around the hair follicle 2 weeks post-treatment, and a significant increase in terminal hair density 3 months post-treatment with PrP. 166][17][18][19] Two studies reported a statistically significant increase in Ki67+ keratinocytes after 2 weeks of treatment. 16,17Rodrigues et al. and Alves et al. reported a positive effect of PrP on anagen hair percentage, but this was not statistically significant. 6,15Mapar et al. looked at terminal and villus hair count only and found no significant improvement. 20Gentile et al.
reported an increase in epidermal thickness 2 weeks post-PrP injection. 17Two studies reported increased patient satisfaction with PrP versus control but did not comment directly on quality-of-life outcomes. 13,14Qian et al measured density and vellus:terminal hair ratio (See Table 2).

| Patient satisfaction
All papers that recorded satisfaction reported an increase posttreatment.Kachhawa et al. used a linear analogue scale to measure patient satisfaction.They reported an average score of 70%.Singh et al. reported a percentage change of satisfaction in all four participant groups, including the placebo.They showed that the group receiving PrP combined with minoxidil had the highest increase in satisfaction.This was followed by the PrP only group, then the minoxidil only group and placebo, respectively.However, there is no validated tool to reliably test satisfaction in this patient cohort, and there was no information reported regarding the method of assessing satisfaction.

| Side effects
The most common side effect was local pain to the scalp.No longterm side effects, or major side effects were reported (See Table 4).

| DISCUSS ION
This is the most methodologically robust and high-quality review on the effectiveness of PrP on male AGA.This review concludes that PrP may be a successful treatment for AGA, particularly with regards to hair density, and is associated with a low side effect profile.Included studies showed consistently that there was a statistically significant increase in hair density in comparison to the placebo.It is difficult to draw a comparison between PrP as an isolated treatment versus combination as different combinations were used in different studies.Singh et al. used four arms to offer a comparison of isolated PrP therapy and combination therapy with minoxidil.They showed that there was no statistically significant difference in hair density between monotherapy and dual therapy, although patients did report a higher satisfaction with the treatment.
All studies included some level of follow-up.[17][18][19][20]  Complications due to PrP injection were minimal and participants reported few side effects to the treatment.Two studies noted that patients reported localized pain following the procedure, but these studies did not use local anesthetic. 14,18Considering the intolerable effects of well-established treatments for AGA, finasteride and minoxidil, and the costliness of hair transplantation, PrP may be a more favorable treatment option for patients. 4,5evious studies have suggested PrP is more efficacious in patients with milder Norwood-Hamilton scores (III-V). 184][15][16][17][18] Mapar et al., who included patients with AGA grades IV-VI, showed no statistically significant improvement in primary outcomes with the use of PrP. 20Therefore, our review upholds these claims. 185][26][27][28][29][30][31][32] All of these systematic reviews showed deficiencies when analyzed using the AMSTAR-2 criteria.Common weaknesses of other systematic reviews included lack of a priori research protocol, incomprehensive literature search strategy, poor screening strategy, and no consideration for study bias.Moreover, F I G U R E 1 Flow diagram of the selection of included papers, as well as reasons for papers excluded with.

TA B L E 1
The characteristics of all papers included in the study, including study design, number of participants, and risk of bias.Risk of bias was measured using the Cochrane Risk of Bias Tool, or ROBINS-I depending on study type.b "The relapse of androgenic alopecia in all patients was not evaluated until 12 months after the last treatment.Four patients reported progressive hair loss that was more evident 16 months after the last treatment.Those four patients were treated again with three PrP injections."

Norwood
c Regen and Arthrex were two processing systems, the results were combined at 6 months, then separated at 6 months.
no reviews have looked exclusively at the use of PrP in male patients with AGA.
The topical use of platelet concentrates is recent, and its efficiency remains controversial.Furthermore, there is no standardized preparation protocol and different concentrations have been shown to actuate different biological effects. 34Despite this, PrP is being used to assist in regeneration of tissues in various parts of the body including hair growth, scar damage repair, and the musculoskeletal system. 34The key components of PrP, that relate to hair regeneration, are platelets, leukocytes, and fibrin.Leukocytes play a role initiating the regeneration cascade, that repairs dead or damaged hair follicles, along with other key molecules (including platelets, cytokine granules, and many other cytokines that work synergistically). 35Fibrin is the activated form of a plasmatic molecule called fibrinogen. 36It is naturally occurring in plasma and plays a vital role in cell migration and proliferation of cells, including hair follicles. 37P contains components that naturally occur within the blood and that are familiar to the body.This explains the low side effect profile that was found in this review and echoed in previous studies.

| Limitations
There are some limitations to this systematic review.We intended to evaluate the efficacy of PrP injections in males with AGA only using high quality evidence.However, our strict quality criteria left nine single-center studies which met the inclusion criteria.Additionally, we included several primary outcomes in our review; however, there was variation between papers in outcome definition and measurement and many had not measured all outcomes pre-defined in our review.The studies also varied in study design including varying treatment protocols.Two out of eight studies measured subjective patient satisfaction (however, both with unvalidated questionnaires), whereas the rest did not.The substantial heterogeneity between studies prevented meta-analysis and increased the difficulty of compiling the results into a cohesive conclusion.
Furthermore, there is a potential risk of compounded bias in this review.Studies ranged in their GRADE score, with eight studies included considered moderate quality evidence and one study considered poor.
Moreover, seven out of nine included studies were concerning for bias, according to the Cochrane risk of bias tool. 11Variation in randomization, selection and reported outcomes can all compound potential bias, and the quantitative effect of this in the review is unknown.
There was also substantial variation in extraction protocols and definitions of PrP.There is currently no standardized protocol and PrP varies widely in exact quantities of components, such as growth factors and platelets. 38Gentile et al. analyzed the effects of inactivated PrP versus placebo and found beneficial effects. 17This may indicate that the addition of activating agents may be unnecessary.Rodrigues et al. analyzed the levels of growth factors in each quotient of PrP and measured hair count, hair density, and percentage of anagen hairs, and found no association between varied growth factors and clinical outcome. 15e study was unable to conduct a meta-analysis due to the large heterogeneity between studies.This limits the ability to critically compare the treatment regimes.The large discrepancy between studies indicates that there is no consensus on the most effective treatment protocol.Further studies are needed to evaluate this.
The study focused on autologous PrP only.Homologous preparations, out of the scope of this paper, are also available and have been shown to increase hair density too.They may be more effective than autologous preparations, though further research is needed to establish this. 39

| Future work
As discussed previously, there were inconsistencies in preparation protocols of PrP, follow-up length and treatment regimes.This TA B L E 4 The side effects experienced by participants of each study included in the review.
demonstrates that there is no clear evidence to advise practitioners of the most efficacious regimes and protocols.Further studies are needed to investigate the optimal preparation of PrP to optimize cell regeneration; however, there may need to be multiple concentrations, adjusted according to the area of intended use.
Further long-term studies are also needed to evaluate the potential transient nature of PrP in some participants, and overall long-term effects.

| CON CLUS ION
In conclusion, PrP is a promising potential therapy for AGA.However, the lower quality of evidence and moderate risk of bias of studies included in this review make it difficult to make any firm conclusions regarding the use of PrP in the treatment of AGA.We recommend further robust long-term studies of this intervention, with larger randomized patient cohorts and standardized treatment protocols.
Relevant studies published from August 2011 to August 2022 were identified by systematically searching MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL), CINAHL, Clini calTr ials.gov, Google Scholar, and Science Citation Index databases.References of included articles were screened and any additional eligible articles were reviewed.The search was repeated in November 2022 to identify recently published relevant articles.The search strategy combined terms related to AGA and PrP.
Dicle et al were deemed to have low risk of bias.14,18Mapar et al, Rodrigues et al, Gentile et al (2015), Gentile et al (2017), Alves et al and Qian et al were all deemed to have some concern for risk of bias.
Gentile et al. followed patients up for 2 years and noted 4 out of 23 patients reported a progressive hair loss 16 months post-treatment.This suggests that, for a small cohort of patients, the benefits of PrP are transient.Patients may then need further courses of PrP injections for AGA, raising the relative cost of treatment.The variation in follow-up and measurement intervals, however, increases the heterogeneity of studies and therefore it is difficult to draw a conclusion about results at each time point.

6 TA B L E 3
Total change in outcome parameters from initial assessment to the end of the follow-up period.

a
All values are from initial assessment before the first injection, to the final follow-up period unless stated otherwise.

Authors Hair count/cm 3 Hair density count/ cm^3 Vellus hair density/ (1/cm 2 ) Terminal hair density/ (1/cm 2 ) Vellus to terminal hair ratio/% Mean thickness/mm Hair growth rate/ mm/day
19chhawa et al.13"During application, almost all the patients felt pain, despite local anesthesia, which subsided after 4 h.None reported any increase in hair shedding, any infection or ecchymosis.No major side effects [reported]"Singh et al.14100% of patients reported instant pain post injection, no pain reported in follow-up sessions Mapar et al.20Side effects not evaluated Rodrigues et al.15Side effects not evaluated Dicle et al.18"The most common discomfort due to treatment during PRP injections was local pain.No other side effects were observed" Gentile et al.16"No side effects were noted during treatment"Alves et al.6Side effects not evaluated Gentile et al.17Side effects not evaluatedQian et al19"The side effects were minimal pain, redness, and pinpoint bleeding after instant PRP injection.No other major side effects were reported during treatment"