Diagnostic Techniques and Clinical Documentation
The pull test is an examination that is easy to perform and to repeat, to roughly judge active hair shedding. Briefly, 50–60 hairs are grasped by thumb, index and middle fingers. While the hairs are tugged away, the fingers slide along the hair shaft. The pull test is positive when more than 10% of the grasped hair can be pulled out. The test has a large inter-observer variation and is influenced by shampooing so that each examiner should personally standardize their own procedure. The pull test should be performed in the right and left parietal, frontal and occipital regions and in the visibly affected areas, as shortening of the cycle increases telogen rates and the pull test becomes positive. The pull test in different scalp regions is useful in excluding diffuse effluvium.
In patients with AGA the pull test is positive only in the active phase with increased telogen hairs in the affected area. It may be frontally accentuated or diffusely positive. A diffuse positive pull test requires further diagnostic tests to exclude diffuse telogen effluvium.
The pull test is usually negative in AGA, except in active periods when there can be a moderate telogen hair shedding in a pattern distribution. However, even with a diffusely positive pull test such as in telogen effluvium or diffuse alopecia areata, underlying AGA may be present.
Dermoscopy or Loupe
Dermoscopy or loupe are noninvasive techniques, which improve examination of scalp skin and hair by magnification, e.g. assessment of hair follicle openings to exclude scarring alopecia is facilitated. In combination with video mounting (videodermoscopy) the storing of diagnostic findings for further controls can be taken into account.[36,45]
In AGA increased hair diameter diversity and an increased number of vellus hairs can be seen. Less common are peripilar signs, reflecting the presence of perifollicular infiltrates, and yellow dots more prevalent in alopecia areata.
Global photographs are helpful tools to evaluate objectively the course of hair growth, hair volume and hair density in clinical studies and for long-term follow-up in daily practice. In clinical studies the photographs of vertex, mid-pattern, frontal and temporal regions are standardized by using a stereotactic device assuring a constant view, magnification and lightening for follow-up assessment. It was agreed that global photography is suitable for daily clinical practice only when a standardized technique is used.
Automatic Digitalized System for Hair Density and Anagen/Telogen Hairs (Phototrichogram/Trichoscan)
These systems for measurement of hair density and the anagen/telogen ratio can be used for diagnosis and follow-up, where available, but their use is mainly as a tool for clinical studies. In AGA the frontal hair density is decreased compared with the occipital density. The anagen/telogen ratio is normal or decreased. To ensure reproducibility, tattoos identifying the area are required. These techniques are helpful for long-term follow-up and quantification.[48,49]
The trichogram is indicated only in individual cases where a loose anagen syndrome or anagen-dysplastic effluvium is suspected. A trichogram should be used only by dermatologists who are familiar with this technique and perform it routinely.
The scalp biopsy is an essential instrument in the diagnosis of cicatricial and selected forms of noncicatricial alopecia. A biopsy, mostly performed as a 4-mm cylindrical punch, is indicated in AGA only in cases where the diagnosis is uncertain, e.g. where scalp changes suggestive of cicatricial alopecia or diffuse alopecia areata are present. Scalp biopsies should be reported by dermatopathologists who are experienced in hair pathology using both vertical and horizontal sectioning.
Site of Biopsy The preferred area for biopsy is the central scalp in an area representative of the hair loss process. Biopsies should not be taken from the bitemporal area as this region may have miniaturized hairs independent of AGA.
Type of Biopsy Two 4-mm punch biopsies following the direction of the hair shafts are taken lateral to the midline deep into the subcutaneous fat where anagen hair bulbs are located. One biopsy is processed for conventional vertical sectioning; the other is sectioned horizontally with respect to the skin surface.[51–53]
Horizontal sectioning allows a rapid assessment of hair follicle numbers, diameter, grouping and morphology. In AGA, there is an increased number and proportion of miniaturized (vellus-like) hair follicles. The ratio of terminal to vellus-like hair follicles is typically < 3 : 1 in AGA-affected areas compared with > 7 : 1 in the normal scalp. Other features include an increased telogen : anagen ratio and an increase in the number of follicular stelae (tracts beneath miniaturized follicles). A mild perifollicular lymphohistiocytic infiltration primarily around the upper follicle as well as perifollicular fibrosis may also be seen.
The British Journal of Dermatology. 2011;164(1):5-15. © 2011