Assessment of hair loss: clinical relevance of hair growth evaluation methods
Clinical and Experimental Dermatology
Volume 27 Issue 5 Page 358-365, July 2002
Hair evaluation methods
Invasive methods
Scalp biopsy examination is the best example of an invasive method. The sample is processed in a laboratory set up for scalp histology such as horizontal sectioning (parallel to the skin surface).2,3
Horizontal sectioning allows the study of a large number of follicular structures including the fibrous tracts, which are often difficult to see on vertical sectioning. Inflammatory infiltrates are more easily seen and their relationship to the follicular structures is more obvious than in vertical sectioning. A trained observer will easily stage the hair follicles into anagen, telogen or catagen. Because of its high magnification, quantitative microscopic analysis of scalp biopsy specimens may serve the purpose of validating other measurement methods.4 For example, we demonstrated that total serial sectioning − from top to bottom (i.e. several hundreds of sections) – is required for the full picture. By doing so, one also realizes that a hair fibre may remain for some time in the follicular ostium − at the end of telogen and exogen stage − which further complicates analysis between hair counts and hair follicle counts. This view is also shared by other observers (D. Whiting, personal communication).
Hair density or number of hair follicles per unit area, is usually reported as number/cm2. It reflects the number of functionally active follicular units whether growing or not. Under physiological conditions, we know that most follicles will produce visible hair at the scalp surface but this may change dramatically in scalp and hair disorders. Hair follicles remain in the scalp and a follicular opening tells of the presence of a potential follicle. The percentage of anagen follicles reflects the time during which hair follicles are engaged in the growth phase. This is true only when an exhaustive count of follicles is made, i.e. including those that are not visible at the scalp surface (anagen III–V) and those that are subject to miniaturization. As mentioned already, this requires complete serial sectioning and accounting of hair and of hair follicles, which is generally a painstaking exercise.
The biopsy is very valuable in the search for interfollicular inflammatory changes and identification of subtle changes in the structure of the skin. It is of more limited interest in the functional exploration of dynamic processes of individual hair follicles. This is because scalp samples are small; a 4-mm punch biopsy has an area of 0.126 cm2, so they contain a small number of hair follicles (one hair may represent as much as 5% in a normal scalp sample). Also, as the tissue is removed it cannot for obvious reasons be re-examined later on for functional modifications.
Semi-invasive methods
Hair root analysis (also named trichogram) is a typical example of the semi-invasive methods still popular in some European Countries.5 According to advocates of the method, the test should be performed 5 days after shampooing. This can be unpleasant for patients with current standards of scalp hygiene. Additionally, the method requires passive accumulation of shedding hair in order to detect hair loss. We speculate that the method is too highly sensitive to the transit from telogen to exogen and reflects more the latter transitions rather than measuring transitions between anagen and telogen. Due to the relative values generated (telogen :anagen ratio) and the lack of exhaustive sampling this technique is generally a poor indicator of disease activity and/or disease severity especially in androgen-dependent alopecia and as documented in women.6 We discourage its use in the clinic and have always rejected the use of the trichogram for efficacy trials.
A different approach is the unit area trichogram. This is performed after 1 month of regular shampooing (e.g. twice a week); the last shampoo is usually performed on the day of the visit. It is a technique in which all the hairs within a defined area (usually 60 mm2) are plucked. Besides the usual hair measurements such as hair density, anagen percentage, hair length and hair diameter there is also an interesting dimension of ‘cosmetically significant hair’. This is a hair with a defined thickness and length (e.g. > 40 µm and at least 3 cm long). Fashion may however, limit the application of the method depending on what hair style is desirable for the patient (e.g. a close hair cut is the currently popular style compared with longer hair in 1970).
The unit area trichogram has been evaluated in terms of reproducibility and clinical relevance. As an example of its use in open drug trials in men7 the unit area trichogram data tends to confirm hair maintenance with minoxidil topical solution as opposed to the natural progression of androgenetic alopecia in men. The induction of hair regrowth with finasteride in men is also reported7 and confirms results obtained with other hair growth measurement methods.8,9 After compensation of initially depleted iron stores in women with chronic telogen effluvium the unit area trichogram also effectively demonstrated reduced telogen rates.7
The technique has also been used for comparative purposes. Most hair growth variables that are estimated through unit area trichogram and the phototrichogram appear comparable and lead to significant improvement of the phototrichogram technique10 (see next section).
Non-invasive methods
In the description of noninvasive methods we distinguish between global and analytical methods. Global methods combine various factors responsible for the hair area under examination but cannot resolve details as opposed to the analytical methods. The latter provide a series of individual measures that reflect the structure and function of the hair follicle as an organ. Such data are subject to critical analysis. By combining all the analytical data one can generate a global value but the reverse is untrue. Also another disadvantage of published global methods is that they are usually not calibrated and from the statistical point of view, the differences in categories are unequal. The use of calibrated systems may provide some answers.
Global methods
Categorical classification systems. Distinctive patterns of defective scalp skin coverage or alopecia have been identified by clinicians as patterns more or less specific for male and female patients.11,12
Static by definition such diagrams (one example in Fig. 2) do not help in measuring the dynamics of hair changes − whether growth or loss − over time. In order to circumvent the lack of control over the involved areas the top of the head can be divided into a number of fixed and predefined subunits (Figs 2 and 3) and some results obtained with this novel approach will be discussed in the next section.
Calibrated scalp coverage scoring. A system has been developed in which examination of the scalp surface proceeds through fixed external standards. The top of the head is separated into small units (equal size in the projection plane) with no anatomical correspondence to the bones of the skull (e.g. frontal, parietal, etc.). The relative difficulty (score 0 when there is no difficulty and 5 when it is barely possible) in detecting scalp skin between the hair is translated into scalp coverage scores. This is rated against objective measures of density (method and equipment for measuring coverage density of a surface: Skinterface, application patent n° PCT/EP 01/06970, 2001). During calibration studies, the scalp coverage scores were correlated with clinically relevant hair parameters such as proportion of anagen hair or density of thinning hair13 and the reproducibility (intra- and interobserver) is very high (correlation coefficients > 0.9). The method allows quantification of clinically relevant changes in real time (Fig. 3). The main advantage of the scalp coverage scoring method is its ease of use in the hair clinic. It helps to measure the continuum of scalp coverage as a criterion of severity of alopecia before inclusion of a patient into a clinical trial, or it can measure changes in subjects as they respond to specific treatment regimens (personal unpublished data).
Global photographs. Global photography has been a significant step forward in scalp hair documentation by creating a permanent record. It combines all factors involved in hairiness, provided that adequate scalp preparation and hair style are maintained throughout the study.14 Paired comparison of global photographs (before and after treatment) is a more precise appreciation of hair growth after drug treatment compared with subjective evaluations of investigators and patients.15
Daily collection of shed hair. The cyclic hair growth activity results in a daily shedding process in which telogen hairs are shed and leave an exogen follicle which is, ideally, to be replaced by anagen stage resulting in visible hair at the scalp surface. The reported normal average daily loss of hair ranges somewhere between 40 and 180 hairs but our average in control subjects are closer to the lower values (personal unpublished data).
In a study of 404 females without hair or scalp disease, daily lost hair was collected over 6 weeks with the aim of comparing two shampoos. Results showed that mean hair loss rates ranged from 28 to 35 per day. No significant differences were noted in the mean daily hair loss rates during the 2 weeks baseline and the 4 weeks treatment period.16
Quantifying daily hair loss in women was assessed in another study of 234 women complaining of hair loss among whom 89 had apparently normal hair density. The researchers found that subjects with normally dense hair (though complaining from hair loss) shed fewer than 50 hairs a day.6 So the magic number of 100, so often referred to in textbooks and found in the lay press, should be seriously revisited. Fewer than 50 hairs can be significantly abnormal in a patient having lost 50% of his hair (personal unpublished data).
Hair weight and hair count methods. The natural progression of hair loss and the efficacy of hair growth promoting agents can be established by comparing the total hair mass (weight) of hair that is produced during a certain period of time. Mass reflecting production and hair counts of grown hair can also be evaluated in a small, carefully maintained area of the scalp. One does not generate staging of growth phases of individual follicles but the technique reveals drug effects and between-treatment regimen differences (example 2 vs. 5% minoxidil).17 One must be aware of the technical skills necessary to handle the scalp sites and clipped hair samples properly. Since the introduction of this method, the authors never alluded to the possible edge effects where a small drift may significantly contribute to a relative increase of the mass of hair that is being produced over time especially when an active compound is tested.
An improvement of hair counting was achieved by using close-up macrophotography of a clipped scalp site. Hair counts reflect ‘visible’ hair even though the exact meaning of ‘visible’ was neither provided nor measured against other methods.14 Increased hair counts as observed with finasteride in androgenetic alopecia in men, is correlated with global perception of improved hair growth with other subjective and objective measurement methods.15 This most probably reflects anagen induction and maintenance as shown when close-up photographs are taken repeatedly at a shorter time interval, e.g. 72 h.8 This latter method is yet another variant of the phototrichogram that will be discussed in greater detail below.
Hair pull test. This is based on the idea that ‘gentle’ pulling the hair brings about the shedding of telogen hairs.6 Besides the fact that this concept remains speculative, it is a very rough method and difficult to standardize as it is subject to so much interindividual variation among investigators. Physically speaking, the pulling force is not distributed uniformly all over the whole hair bundle which creates variation in the pulling force from one hair to another. It seems to be useful only in acute phases of hair loss in the more severe conditions (drug-induced hair loss, alopecia areata, etc.). At least, we do not advise that important diagnostic, prognostic or therapeutic decisions are made on a hair pull test in the most common conditions such as chronic telogen effluvium or patterned (male or female) alopecia.
Analytical methods
Phototrichogram. The basic principle of the phototrichogram consists of taking a close-up photograph of a certain area of the scalp. The hair is cut very close in preparation for the first photograph, followed by repeat photographic documentation after a certain time period. This period of time should be long enough to permit the evaluation of the growth of a hair segment (which is usually between 24 and 72 h) but not too long in order to prevent outgrowth or too much overlapping of growing hair. The growth is then evaluated by comparing the two pictures. Hairs that have grown are in anagen phase; those which have not are in telogen phase (Fig. 4).
Phototrichogram techniques are subject to continuous re-evaluation and improvement10,18,19 and phototrichogram data have been computed for mathematical modelling so as to simulate patterns of defective hair replacement similar to those observed in the hair clinic.20 Nevertheless, not all productive hair follicles are taken into account during the usual phototrichogram procedures. Accordingly, we recently developed and validated the contrast-enhanced phototrichogram technique (contrast enhancement phototrichogram) which had a resolution equal to that of transverse microscopy of scalp biopsies and traced, on a follicular basis, all transitions of thick and thinning follicles from anagen through catagen into telogen phase.4 In early stages of androgenetic alopecia (AGA) in man, this sensitive method was able to detect a subclinical phase of AGA with obvious shortening of the anagen phase in the absence of hair miniaturization until the follicular regression process finally turns into production of clinically nonvisible hair.21 The contrast enhancement phototrichogram method has been used for calibration purposes in the case of scalp coverage scoring as described earlier.
One of the main advantages of the phototrichogram is that it is a patient-friendly method. Also it is a totally noninvasive method so it does not affect by itself the natural process of hair growth/loss.
Variants of phototrichogram methods. Subtle modifications in the preparation of the target site can help to compensate for less than optimal conditions to distinguish between the hair in the growing and resting phases.14 Indeed after clipping the hair short (first step of the phototrichogram as a control for density or hair counts of ‘visible hair’), a close shave will further reduce the visible length of the hair fibre. Three days later (instead of 2) the second photograph is taken. A new hair count is made of ‘visible hair’, i.e. only the long hair fibres that reflect anagen hair follicles. This procedure has been used to monitor changes occurring after finasteride treatment in man with AGA demonstrating a significant induction of growth as compared with a placebo.8
When the photographic camera is replaced by a video or CCD camera equipped with specific lenses, other variants of phototrichogram recording are obtained. Reports in Orientals and Caucasians were published and in the latter subjects the contrast between hair and scalp seems favourable for the application of this method and the low figures of hair density could possibly be racial in origin. However the authors advise that these factors are taken into account in order to keep the biological variation as low as possible.22 The use of contrast enhancement is advisable for Caucasian hair and the use of computer applications for hair recognition software has been proposed.23 Promoters of the method recognize that the explored area is small (< 0.25 cm2 for hair calibration).
This is yet another source of variability because the number of hairs so analysed is definitely below 10024 and drops below statistically acceptable population sample sizes. This may explain why the method appears unable to measure loss in placebo-treated subjects. Fully automated analysis systems23,25 remain generally unsatisfactory when detailed description of hair variables such as hair counts, diameter − especially for thinning hair – and growth rate is required. Biologically significant source data in terms of follicle distribution and productivity are not reported. More work needs to be done before such systems reach the status of medically acceptable diagnostic–prognostic and therapeutic monitoring tools.