Methods of evaluating hair growth


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Methods of evaluating hair growth

  1. 1. Australasian Journal of Dermatology (2003) 44, 10–18 PERSONAL REVI EW Methods of evaluating hair growth Alexander J Chamberlain and Rodney PR Dawber Department of Dermatology, Churchill Hospital, Headington, Oxford, United Kingdom over the last two decades would have occurred at all. SUM MARY Although sophisticated computerized techniques pioneered by the wool industry are now available to quantify the For decades, scientists and clinicians have examined various parameters of hair growth, the intrinsic complexity methods of measuring scalp hair growth. With the of hair growth itself has been the main obstacle to the development of drugs that stem or even reverse the development of simple office-based assessment tools. The miniaturization of androgenetic alopecia, there has aim of this review is to outline the various methods available been a greater need for reliable, economical and for the measurement of hair growth, their limitations and minimally invasive means of measuring hair growth their value to the clinician. and, specifically, response to therapy. We review the various methods of measurement described to date, THE HAIR CYCLE their limitations and value to the clinician. In our opinion, the potential of computer-assisted technology Much of our understanding of hair growth is based on in this field is yet to be maximized and the currently animal studies.1 The dynamics of the hair cycle not only available tools are less than ideal. The most valuable differ between species and race but also with age, gender, means of measurement at the present time are global body site and across seasons. Physiological or pathological photography and phototrichogram-based techniques states such as pregnancy, malnutrition or malignancy can (with digital image analysis) such as the ‘TrichoScan’. also modulate hair growth. The total number of follicular Subjective scoring systems are also of value in the units on the human scalp is approximately 100 000–150 000 overall assessment of response to therapy and these and it is generally accepted that this number is fixed and are under-utilized and merit further refinement. does not increase. These follicles are quite evenly distributed over the scalp and most typically in groups of three. Although Key words: androgenetic alopecia, epiluminescence these small groups grow in phase, the growth of scalp hair microscopy, phototrichogram, scalp photography, on the whole is asynchronous or mosaic. Hair follicles trichogram. undergo active growth (anagen) in a cyclic fashion, with this phase typically lasting 3–7 years on the scalp vertex. Anagen has traditionally been divided into six stages of development, from the onset of mitotic activity within the secondary hair INTRODUCTION germ (anagen-I) to the fully developed follicle that first Many methods of evaluating the growth of hair have been emerges beyond the skin surface (anagen-VI). After a brief described by both scientists and clinicians alike. While the transitional phase (catagen) hairs enter a resting phase majority of these methods have been developed to progress (telogen) lasting weeks before being shed. This process then the understanding of normal hair physiology, the discovery repeats itself over and over. At any one time, 85–90% of scalp of agents that promote hair growth has necessitated the hairs are in anagen, with the majority of the remainder in development of reliable and reproducible means of assessing telogen. The growth rate of the hair follicle is fairly constant, hair loss and monitoring response to therapy. Indeed, the averaging about 0.5 mm per day on the scalp vertex and a majority of techniques developed to date have followed the little less at the margins. discovery of minoxidil and its application in androgenetic alopecia (AGA). Without this revolution, it is unlikely that DIMENSIONS OF HAIR GROWTH much of the intense hair growth research and innovation It is important to define the dimensions that constitute hair growth before one can begin to interpret the various methods of its measurement. The basic biological parameters of hair Correspondence: Dr Alexander J Chamberlain, Clinical Research growth include rate of linear growth, hair shaft diameter, Fellow, Department of Dermatology, Churchill Hospital, Old Road, hair density and hair-cycle status. The anagen : telogen ratio Headington, Oxford OX3 7LJ, UK. Email: (or percentage of anagen-VI hairs) is the best measure of Alexander J Chamberlain, MB BS. Rodney PR Dawber, FRCP. cycle status given the impracticalities of measuring the Submitted 27 March 2002; accepted 15 August 2002. duration of anagen, which relies on long periods of
  2. 2. Methods of evaluating hair growth 11 observation and identification of individual hairs. Pigment growth in men with AGA been developed.2 This question- content must also be considered a variable of some biological naire was developed in the Merck Research Laboratories and significance in the study of alopecia. has already been used to supplement clinical measures in It is crucial to recognize that the parameters of hair growth trials examining the effects of finasteride.3 The questionnaire that are of major interest to the scientist are different to those consists of five questions that address patient perceptions of of the clinician or the patient. While much of the recent hair growth and satisfaction with hair appearance. The scientific research in this area has concentrated on the scores have been shown to correlate with hair counts, albeit mechanisms that control the activity of putative follicular modestly. This subjective measure is probably a useful stem cells, the parameters more likely to be of value to adjunct in the assessment of response to therapy. While this clinicians are diameter, density and cycle status. In contrast, questionnaire was designed to assess the perceptions of men, the primary concern of the patient is reduction in density, it would not be difficult to adapt this so that it were applicable which is frequently expressed as ‘loss of body’. The patient to women also. who is losing hair may also report an increase in shedding The manual collection, counting and weighing of hairs (‘hair is falling out’), a reduction in growth rate (‘hair doesn’t shed on a daily basis is a simple technique that can be used need cutting as often’), or a reduction in diameter (‘hair is to follow the progression of hair loss.4 Studies of this type finer’). Of course, the presentation of AGA is quite different have estimated that the average number of hairs shed daily in women and men. Unlike a woman with diffuse hair loss is about 100, a figure that appears widely in hair literature in whom the diagnosis may not be immediately clear, a man and is probably an overestimate for healthy young adults. presenting with a patterned alopecia is usually all too This crude method is not only extremely tedious but requires familiar with ‘common baldness’ and presents requesting careful standardization of collection technique and hair care. treatment rather than a diagnosis. Hydration and seborrhoea are factors that affect hair weight, At present, there is no ‘gold standard’ in the area of so these must also be standardized if this technique is to be measurement of hair growth. The ideal measure would be applied in clinical trials. non-invasive, simple to perform, reproducible, economical, There are a number of grading scales that exist for the and able to integrate all of the basic biological parameters of classification of AGA. It was Hamilton in 1951 who first hair growth as well as to provide information that is subdivided the patterning seen in men with AGA into types meaningful to the patient. The vast majority of the methods I–VIII on a visual scale.5 This system of classification was of measurement that will be discussed here have been later modified by Norwood in 1975 who added four further studied in AGA. intermediate grades: IIIa, III vertex, IVa and Va.6 Although These methods of measurement are equally applicable to the Norwood–Hamilton scale has been used extensively in other non-scarring alopecias, with the exception of patchy clinical trial evaluation, this system is too crude to reliably alopecia areata, in which areas of hair loss are well-defined document response to therapy. In reality, the progression of and regrowth is easily identified; therefore accurate AGA or indeed regrowth with therapy occurs over a con- measurement is not as crucial to the clinician. In scarring tinuum rather than in a stepwise manner. This scale prob- alopecias, histology is vital for diagnosis but quantitative ably still has a role in the broader classification of severity of estimates of hair loss are again not as important. In both AGA in men, particularly in the identification of those who alopecia areata and scarring alopecia, clinical examination are more likely to respond to therapy. and global photography provide the information of greatest In 1977, Ludwig proposed a grading scale for women with relevance, although a more detailed discussion of this issue AGA.7 He suggested types I–III that represented a range of can be found elsewhere and is beyond the scope of this diffuse alopecia over the crown in the so-called ‘female review. The ideal frequency of measurement in the monitor- pattern’ that spares the frontal hair line. It is well recognized ing of hair growth in response to therapy is another factor in that a certain percentage of women develop AGA in the ‘male the equation that is yet to be established. On the basis of pattern’, particularly postmenopausal women.8 telogen duration, many clinical trials have chosen to Savin has expanded on the original grading systems with measure response to therapy at 4-monthly intervals, and his pattern and density scales for classifying AGA in both this is probably the minimum interval at which changes men and women (Fig. 1).9 In men, the appearance of the may be detected. As any expected changes in hair thinning frontal scalp, mid area and vertex are ranked parameters will be small if at all, it is probably prudent to F1–F6, M1–M5 and V1–V7, respectively. Female-pattern AGA assess at 6–12-monthly intervals until a trend has been is divided according to the width of the central part. Density established. The various methods of measurement of hair in both sexes is also graded on the basis of the part (D1–D8). growth have been previously divided into non-invasive, Unfortunately, these qualitative systems are too crude to use semi-invasive and invasive categories and this is a logical in clinical trials for anything more than defining the base- division that we have also chosen to structure our discussion line. They probably have a role in office-based measurement around. until more sensitive tools are widely available and they are certainly significant from a historical perspective. Photography is a very important tool in the clinical NON-INVASIVE METHODS measurement of hair and its dynamics. Global photographs Only recently has a validated and standardized question- of the scalp are clinically relevant in the assessment of AGA naire aimed at the detection of subjective changes in hair because they represent an accurate record of the cosmetic
  3. 3. 12 AJ Chamberlain and RPR Dawber state of the patient. High-quality photographic systems with vertex views were used in the early finasteride trials (Fig. 2).3 stereotactic positioning devices for accurate patient position- It is our opinion that global photographs are a valid method ing are now available commercially.10 Factors such as of hair measurement in the clinical setting, although the best precise combing and lighting are critical to the repro- results are probably obtained in the hands of trained medical ducibility of scalp photographs. The Canfield technique has photographers. recently been validated in a randomized controlled trial In recent years, epiluminescence microscopy (ELM) has examining men with Hamilton III or IV AGA receiving oral been cleverly adapted to quantify hair growth. Epilumines- finasteride or placebo.11 Four standard global views (vertex, cence microscopy is a clinical tool that was originally refined midline, frontal and temporal) are advocated, although only for the diagnosis of pigmented skin lesions, in particular the early detection of melanoma. An European group has created a scoring system based on hair density and diameter as assessed by macrophotographs of a midline part at the vertex of men with AGA (Fig. 3).12 These are performed using a commercially available camera (Dermaphot; Heine Optotechnik, Herrsching, Germany) designed for ELM with 4 magnification. An area measuring 14 13 mm is used to base the measurements. Density is graded on a scale of 1 (fewer than four hairs) to 6 (more than 40 hairs) and dia- meter is graded as 1 (thin), 2 (medium) or 3 (thick). A separate hair diameter diversity scale is graded 0 (<20% in hair diameter diversity) or 1 (>20% hair diameter diversity). They propose that a score of >20% diversity in hair diameter is a useful clinical sign reflecting miniaturization. This is therefore of potential use in the diagnosis of AGA, but prob- ably too crude for monitoring change. Their density and diameter scale has been shown to correlate well with the Hamilton classification and histological hair density. In some ways it can be considered an adaptation of the Savin scale, but localized to a precise point on the vertex and under magnification. A key issue to consider is whether a postage stamp-sized area of scalp vertex is representative of the global effects of AGA on the scalp. Even if it is, this technique is still qualitative and quite subjective, but easy to perform and non-invasive. Figure 2 Schematic representation of stereotactic scalp photo- graphy demonstrating fixation of the subject on a brow and chin rest Figure 1 Pattern and density Savin scales. with the camera mounted on a rotating arm.
  4. 4. Methods of evaluating hair growth 13 The information technology revolution of the late twen- were hair styling and combing, camera-to-scalp distance and tieth century has resulted in advances throughout medicine, contrast between scalp and hair colour. These are short- including hair measurement. The major capability of the comings that the Canfield system has partly addressed computer that has been exploited in the field of hair with standardized combing and patient positioning, although measurement is image analysis and its quantification of the contrast between scalp and hair colour, particularly clinical or even histological appearances. High-speed when it is minimal, is a limitation common to all imaging processing, high-resolution imaging and vast storage cap- systems. acity for archiving are further advantages of computer systems in clinical measurement. A computer-assisted SEMI-INVASIVE METHODS method of estimating hair density has been used to estimate the response to therapy in a patient with diffuse The linear growth rate of scalp hair can be measured in a alopecia areata.13 This involves the digitization of a photo- number of ways. Perhaps the simplest technique is to stain a graphic image of the scalp and could equally be applied to group of hairs using a dye that contrasts with the colour of AGA. Darker shades of grey are interpreted as hair and the native hairs.14 A growth rate can then be calculated by lighter shades as scalp and then the proportion of each dividing the length of unstained hair in millimetres by the variable is calculated. Factors that influenced the results number of days between measurements (mm/day). If Figure 3 Scoring system of hair density and shaft diameter using a magnified photographic scale (repro- duced with permission from Arch. Dermatol. 2001; 137: 641–6, copy- righted 2001, American Medical Association).
  5. 5. 14 AJ Chamberlain and RPR Dawber estimated over a standardized area, the proportion of anagen This involved shaving a small area of scalp hair as well as and telogen hairs can also be assessed, because only the plucking 50–100 hairs using forceps without sharp edges and anagen hairs will show growth. Close-up photography ideally covered with adhesive tape (Fig. 5). The shaved area improves the accuracy of such observations, although con- was examined after 10 days to assess the linear growth rate. ditions must be strictly standardized and there must be The roots of the plucked hairs were examined to provide an sufficient contrast between background scalp and hair estimate of cycle status (anagen : telogen differential) and colour.15 density was assessed using a microscope with 60 magnifi- Alternatively, hairs may be clipped close to the surface, cation and an eyepiece marked with a 1-cm 2 area. Hair shaved or even plucked prior to measuring growth rate, diameter was also assessed microscopically. Originally, hairs although plucking results in a variable delay before the were graded into thick (0.1 mm), medium (0.05 mm) and appearance of a new anagen hair. A designated area can be thin (0.025 mm) categories using calibrated wires for re-clipped, shaved or plucked and then weighed after a set comparison. A final parameter was the ‘regeneration period period to measure regrowth. This technique has been used 90’, which was the time lag in the appearance of 90% of to document normal growth,16 and response to minoxidil in plucked hairs from a given area. This technique was applied women17 and finasteride in men18 with AGA. It has been extensively thereafter to study the hair of subjects of varying proposed that the total weight of hair from a defined area of ages and under various physiological influences.23 While this scalp is an ideal quantitative measure of hair growth for use work helped to define the normal variations according to in clinical trials.17 However, this technique seems just as age, gender and body site, it is now largely outdated as a complex and tedious as other manual methods, requiring research technique in AGA. A further refinement on the careful degreasing, drying and control of humidity to avoid trichogram was the unit area trichogram (UAT), which error. introduced a standardized pre-sampling, washing and Calibrated capillary tubes have also been used to measure combing protocol, and plucking of hairs from within a linear growth rate.19 These are fitted around individual hairs defined area (usually 35–44 mm2) to determine density in a that have been clipped and then pressed gently against the more accurate fashion.24 The major shortfall of the skin surface (Fig. 4). Measurements are daily or even more trichogram is that hairs in early anagen and vellus hairs are frequently. Reference points would clearly be necessary if easily missed in a standard pluck because of their small size. particular hairs were to be followed individually over time. Furthermore, plucking 50–100 hairs is quite a painful pro- Intradermal injection of radiolabelled substances followed cedure for patients to undergo. Plucking is also known to by autoradiography is a research technique that provides an change the natural course of the hair cycle.25 accurate method of marking hairs along their length. 20 The first efforts to document the growth of hair using Linear growth rate can then be measured by dividing the photography at close range were performed on three distance between marks on autoradiographs by the time Japanese men who were studied at regular intervals over a between injections. The small doses of radiation required in period of 2 years.15 Hairs at different body sites including the these assays have been deemed safe in non-pregnant scalp were studied, enabling estimates of the lengths of humans. These techniques are not only labour-intensive but anagen and telogen for each individual. Hairs were kept serial scalp injections are unlikely to be well tolerated by clipped at lengths of 1 mm (whenever photographed) within patients outside a research setting. Linear growth rate is not a small area to allow accurate identification of individual a vital parameter in the measurement of miniaturization. hairs. In the 1960s a compound measurement of the major biological parameters of hair growth was first described.21 This technique was to be known later as the trichogram.22 Figure 4 Hair-growth measurement using graduated scale capillary tubes. Figure 5 Technique for plucking hairs with surgical forceps.
  6. 6. Methods of evaluating hair growth 15 This work formed the scientific basis of the photo- growth. Cells arrested in metaphase are expressed as a trichogram (PTG) that has been refined by several investi- proportion of the entire matrix. This technique has mainly gators.26,27 This technique involves serial magnified been applied to the study of the seasonal variations in wool photographs (Fig. 6) of a target area of scalp hair (1 cm2) over growth.38 However, this also involves administration of a period of days to define which hairs are in anagen (those cytotoxics. growing) and which are in telogen (those not growing). In Histopathological analysis of scalp biopsies has been used addition to cycle status, the PTG enables measurement of for some time now to investigate hair growth. Biopsies are linear growth rate as well as diameter and density. Although performed under local anaesthesia. A 4- or 6-mm punch painless, it is time-consuming and is limited by the same deep into the subcutaneous tissue directed along the slant of inherent problem as other scalp imaging systems of exiting hairs is typically taken from a transitional area differentiating hairs from scalp background. The application between balding and normal scalp and a suture is normally of an immersion oil28 and temporary hair dye29 have required for haemostasis. Although the original descriptions improved this contrast to some degree. Several investigators of this technique involved a single punch, it is more usual to have attempted to automate the process of monitoring hair take two punches at the present time. Early studies of growth via PTG, although overlapping hairs and various macaque monkeys (who develop AGA) using scalp biopsies artefacts have proven to be major obstacles to computerized sectioned vertically along the length of the hair follicle measurement.27,30,31 Assessment of hair diameter is also enabled the construction of histograms known as ‘folliculo- unreliable unless magnifications in the order of 20 are grams’.39 These depicted follicle lengths and proportions of used.32 A computer-assisted image analyzer has been shown anagen, catagen and telogen hairs, and over time were able to enhance the quality and reliability of this facet of to demonstrate the improvement in the terminal : vellus ratio measurement.33 with minoxidil therapy.40 Despite these shortfalls, the PTG has been applied success- It has since been shown that horizontal sectioning fully in finasteride trials to show statistically significant provides greater diagnostic information than vertical sec- increases in density and the anagen : telogen ratio over tions alone.41 This mode of processing provides measures of 12 months in men with AGA.3,34 Increases in hair diameter density, hair-shaft diameter, and the anagen : telogen and have not been able to be adequately documented in these terminal : vellus ratios. Automated computer analysis has trials using the PTG. been successfully adapted to assist with the quantification of The latest modification of the PTG combines ELM with these parameters.42 Both density and terminal : vellus ratios digital image analysis; the ‘TrichoScan’.35 In comparison to have been shown to be useful indices in monitoring the the traditional PTG, this method uses ELM instead of response of AGA to minoxidil43 and finasteride,44 respec- macrophotography, as well as contrast enhancement of hairs tively. A terminal : vellus ratio of less than 4:1 has been with temporary dye. Specially developed computer software suggested as diagnostic of AGA, whereas the ratio in the enables assessment of the four basic biological parameters of hair growth (Fig. 7), with the whole procedure taking 20 min. This technique has already been used to document increases in hair count and cumulative diameter in men with AGA treated with finasteride, over a period of 6 months. The developers of the TrichoScan appear to have drawn on years of PTG research to create a validated clinic-based measure- ment tool that is both elegant and patient friendly. The cost of equipping the clinic with this system is an important outstanding question. INVASIVE METHODS The ultimate measure of hair growth is the examination of matrix cell kinetics. The two main proliferative indices are the mitotic index and the labelling index.36 The former is a count of the number of actively dividing cells at a given point in time, as measured on wax-embedded sections. The latter is a count of the number of cells entering mitosis during a given period, and requires intradermal injections of tritiated thymidine prior to biopsies subjected to light microscopy autoradiography at set intervals.37 These indices are not only invasive, but they only provide a static appreciation of a dynamic process. In addition, thymidine is potentially toxic and therefore unsuitable for repeated administration. The metaphase index, in contrast, provides a measure of the rate of cell production and is more suitable for studying hair Figure 6 Macrophotograph of scalp hair.
  7. 7. 16 AJ Chamberlain and RPR Dawber normal scalp is between 6:1 and 8:1.43 One of the criticisms manner does not appear to be available at the present of this method is that horizontal sections taken at the level of time, despite the intense research into this subject. The the entry of the sebaceous duct will underestimate the total large variety of techniques employed over the decades is number of vellus hairs because many of these are found testament to this conclusion. The ideal tool(s) would be more superficially in the midreticular dermis. 38 able to measure hair-shaft diameter and hair density at a Another histological parameter that has been studied is the microscopic level, in addition to providing a subjective volume of the hair bulb. In animal studies the volume of the assessment of both the appearance and satisfaction of the dermal papilla has been shown to bear a direct relationship patient. to the volume of terminal hair.45 Although this work has been While the UAT and the PTG may be the favoured tools replicated in humans with AGA,46 this parameter has not within the setting of clinical trials, we feel that subjective been used to follow the response of AGA to therapy. scores and global photography are of greater relevance in the The major limitation of these invasive methods in the clinic. A subjective scoring system for women with AGA or study of hair growth is that they do not permit the repeated even a unisex scoring system are yet to be developed and sampling of a consistent area of scalp over time. Further- validated as far as we are aware. In our opinion, the method more, a single 4-mm sample of scalp is not always that shows the greatest promise in the monitoring of AGA adequately representative of the global process because of and its response to therapy is the TrichoScan, although this regional variation.47 is only likely to be financially viable for academic depart- ments (as opposed to the average clinician) at the present time. While the impact of computer-assisted image analysis CONCLUSION has been largely disappointing as far as progressing An adequate means of measuring hair growth in the clinic techniques of hair measurement, we hope that the next over time in a reproducible, economical and non-invasive decade will see the introduction of improved means of Figure 7 Software interface depicting variables of hair growth as measured by the ‘Trichoscan’ technique (reproduced with permission from Eur. J. Dermatol. 2001; 11: 362–8).
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