To the Editor: Androgenetic alopecia (AGA) is widely observed in men worldwide. It can evoke feelings of inferiority by symbolizing premature aging, potentially impacting self-esteem and interpersonal relationships. The progression of AGA is globally assessed using the revised Norwood–Hamilton classification (NH classification).1,2 This scale quantifies the pattern of progression and extent of hair loss, which is crucial for clinical evaluation and treatment decisions. Although AGA is known to progress with age, further research is still needed to address the details of the relationship between the progression of AGA and age3 We hypothesized that there would be significant differences in median age across NH classifications.
This study analyzed data from 5372 male patients aged 20-65 years who visited Tokyo Memorial Clinic between 2006 and 2023. The data were collected by board-certified plastic surgeons with PhD degrees, each of who had over 5 years of experience treating an average of 30 AGA patients per day, 4 days a week. In the NH classification, stages IIa and IIv, IIIa and IIIv, IVa, and Va were simplified into stages II, III, IV, and V, respectively, and the median age for each classification was calculated and compared using the Kruskal–Wallis test, with results presented as medians and 95% confidence intervals using violin plots. Statistical analyses were performed using GraphPad Prism 10 for macOS (Version 10.1.1, November 2023). Fig 1 shows a bar graph of median ages with 95% CI for each NH classification, while Fig 2 shows a violin plot, offering a more detailed visualization of age distribution across NH stages. The median age for NH classification I was 26 years (95% CI 25-27), and as the NH classification increased, so did the median age, with NH classification VII showing a median age of 52 years (95% CI 46-61). Confirming our hypothesis, the Kruskal–Wallis test revealed significant differences in median age across NH classifications (P < .0001). Assuming that AGA progresses continuously from onset, these findings support the notion that AGA advances with increasing age. We observed a median time of 4.5 years for progression between stages, a novel finding in AGA research. These quantitative data on progression rate provide valuable insights for clinicians in predicting disease progression and planning appropriate interventions. Our previous research indicated that age >40 years at the start of treatment and higher NH classification are independent predictors of insufficient response to finasteride.4,5 This study highlights the importance of a treatment approach based on the relationship between age and degree of progression. However, there are several limitations to bear in mind. Clinic bias, reliance on the visual assessment by the physicians for diagnosis, and a patient population limited to a single clinic could affect the generalizability of the results. This study has elucidated the association between the progression of AGA and age. In particular, the finding that progression of AGA from one stage to the next in the NH classification takes about 5 years can help to understand the progression of AGA and to devise individualized treatment plans.
Fig 1.
Distribution of Norwood–Hamilton (NH) classification by age. A bar graph shows the median age of patients by NH classification. The horizontal axis represents the groups by NH classification, and the vertical axis includes error bars representing the median age and 95% confidence intervals (CIs) for each group. The list accompanying the graph shows the median age and 95% confidence interval (CI) values for each NH classification.
Fig 2.
Distribution of age by Norwood–Hamilton (NH) classification. The violin plot shows the age distribution for each NH stage. The width of each “violin” represents the frequency of data points at a particular age. The internal lines indicate the median (longer dashed line) and quartiles (shorter dotted lines).
Conflicts of interest
None disclosed.
Footnotes
Funding sources: None.
Patient consent: The authors obtained written consent from patients for their photographs and medical information to be published in print and online and with the understanding that this information may be publicly available. Patient consent forms were not provided to the journal but are retained by the authors.
IRB approval status: Not applicable.
References
- 1.Norwood O.T. Male pattern baldness: classification and incidence. South Med J. 1975;68:1359–1365. doi: 10.1097/00007611-197511000-00009. [DOI] [PubMed] [Google Scholar]
- 2.Hamilton J.B. Patterned loss of hair in man; types and incidence. Ann N Y Acad Sci. 1951;53(3):708–728. doi: 10.1111/j.1749-6632.1951.tb31971.x. [DOI] [PubMed] [Google Scholar]
- 3.Otberg N., Finner A.M., Shapiro J. Androgenetic alopecia. Endocrinol Metab Clin N Am. 2007;36(2):379–398. doi: 10.1016/j.ecl.2007.03.004. [DOI] [PubMed] [Google Scholar]
- 4.Yanagisawa M., Fujimaki H., Takeda A., et al. Long-term (10-year) efficacy of finasteride in 523 Japanese men with androgenetic alopecia. Clin Res Trials. 2019;5(5):1–5. [Google Scholar]
- 5.Yoshitake T., Takeda A., Ohki K., et al. Five-year efficacy of finasteride in 801 Japanese men with androgenetic alopecia. J Dermatol. 2015;42(7):735–738. doi: 10.1111/1346-8138.12890. [DOI] [PubMed] [Google Scholar]