These articles have been accepted for publication in the British Journal of Dermatology and are currently being edited and typeset. Readers should note that articles published below have been fully refereed, but have not been through the copy-editing and proof correction process. Wiley-Blackwell and the British Association of Dermatologists cannot be held responsible for errors or consequences arising from the use of information contained in these articles; nor do the views and opinions expressed necessarily reflect those of Wiley-Blackwell or the British Association of Dermatologists This article is protected by copyright. All rights reserved. Accepted Date : 20-Feb-2014 Article type
: Clinical and laboratory investigations
Title:
Destruction of the arrector pili muscle and fat infiltration in androgenic alopecia
Running head:
Arrector pili muscle destruction in androgenic alopecia
Authors:
N. Torkamani1,2, N.W. Rufaut1,2, L. Jones1,2 , R. Sinclair1,2
Institutions:
1- University of Melbourne 2- Epworth Hospital, Melbourne, VIC., Australia.
Corresponding Author: Prof Rodney Sinclair Epworth Research Institute, Dermatology Lab.,185-187 Hoddle Street, Richmond, 3121, VIC TEL: +61 0408369362 Email:
[email protected] Funding:
The University of Melbourne Post Graduate Research Scholarship
Conflict of interest:
The authors report no conflict of interest.
What’s already known about this topic? •
Androgenic alopecia (AGA) is the most common hair loss condition in men and women and is largely irreversible beyond a certain degree of follicular regression
This article is protected by copyright. All rights reserved. •
Telogen Effluvium (TE) is a reversible hair loss condition known to have histological features similar to normal hair
•
The arrector pili muscle (APM) connects the follicle to the surrounding skin.
What does this study add? •
The replacement of APM with fat tissue is a consistent feature of AGA.
•
Replacement is more extensive in smaller follicles, suggesting that it is a progressive process associated with miniaturization.
Abstract
Background. Androgenic alopecia (AGA) is the most common hair loss condition in men and women. Hair loss is caused by follicle miniaturization, which is largely irreversible beyond a certain degree of follicular regression. In contrast, hair loss in telogen effluvium (TE) is readily reversible. The arrector pili muscle (APM) connects the follicle to the surrounding skin.
Objectives. To compare histopathological features of the APM in AGA and TE.
Methods. Archival blocks of 4 mm scalp punch biopsies from 8 patients with AGA and 5 with TE were obtained. New 4 mm biopsies from 5 normal cases were used as controls. Serial 7 µm sections were stained with a modified Mason’s trichrome. “Reconstruct” software was used to construct and evaluate three-dimensional images of the follicle and APM.
Results. The APM degenerated and was replaced by adipose tissue in all AGA specimens. Remnants of the APM remained attached to the hair follicle. There was no fat in the normal skin specimens. Fat was seen in 2 of 5 TE specimens, but could be attributed to these
This article is protected by copyright. All rights reserved. patients also showing evidence of AGA. Quantitative analysis showed that muscle volume decreased and fat volume increased significantly (P7 is highly in favour of TE. T:V values between 4:1 and 7:1 is usually interpreted as TE with early stages of AGA3. The arrector pili muscle (APM) comprises of a small band of smooth muscle that connects the hair follicle to the connective tissue of the adjacent upper dermis. The APM mediates thermoregulation by contracting to elevate hair shafts, thereby increasing air-trapping and
This article is protected by copyright. All rights reserved. hence insulation. It was thought to be vestigial in humans, but recent studies suggest that the human APM plays an important role in maintaining follicular integrity by holding together each of the hair follicles in the follicular unit at the isthmus level4. Previously it was thought that each hair follicle is attached to a separate APM, but this has been refuted by more recent studies. Clifton et al. demonstrated that branching of the APM in the FU, and that it was inserted into all the hair follicles of the FU 5. In addition Poblet et al.6 studied crosssectional features of the APM using Masson’s trichrome technique and proposed that all follicles within the same follicular unit shared an arrector pilli muscle6. The authors also suggested that AP muscles converge into a muscular unit that is associated with each follicular unit6.. The proximal APM attaches via a tendon to the bulge, a known stem cell niche7,8. Tiede et al. (2007) described an outer root sheath protrusion, the trochanter, in the area of APM insertion9. Narisawa et al.10 have demonstrated the presence of knob like swellings and villous projections in human terminal and vellus hair follicles. The authors also demonstrated the presence of skirt like projections in small vellus hair. These projections were present in small vellus her but not in large ones. Bulge cells interact closely with the APM. The APM-bulge connection persists throughout the hair growth cycle and has been suggested to play an important role in morphogenesis and renewal of hair follicles11,12, 9. In a study conducted by Song et al. the structure of APM was evaluated by three dimensional (3D) reconstructions13. They confirmed some of the findings by Poblet et al. (2002) and in addition they reported that two follicular units can share a single APM as a variation. They also suggested that only one muscular structure is involved in the follicular unit which insets tightly to the furthest follicle14. Through 3D investigations on the APM and follicular units Song et al. reported that all the hair follicles in a follicular unit share the same APM forming a concave support for the sebaceous lobules15. These lobules are located between the follicles and APM, forming an angular area. The sebaceous lobules are also localized in the counter angular area.
This article is protected by copyright. All rights reserved. Limited studies have been directed towards the APM structure in alopecia. Yazdabadi et al.16 found that the APM remains connected to the bulge of miniaturized follicles in alopecia areata but not in male and female AGA. The authors could not define whether APM regression in AGA was a cause or an effect of the disease. Shum et al studied the efficacy of three dimensional image reconstructions in the study of scalp biopsies from patients with non-cicatricial alopecia. The authors demonstrated that 3D reconstruction techniques are an accurate and concise method to study histopathological changes as tissue loss and gaps become significantly limited17. No other study has evaluated the APM in hair loss conditions. We studied the histology and anatomy of the APM in AGA and TE patients compared with normal controls. We found that the APM degenerates in AGA and is replaced by adipose tissue.
Materials and Methods
Patients
This project was approved by the St Vincent’s Hospital Ethics Review Board (Melbourne, Australia). We obtained 13 archival scalp biopsies from patients diagnosed by the Dorevitch Dermatopathology Laboratory (Melbourne, Australia). All scalp biopsies were taken from the vertex region of the scalp. The specimens included 8 cases of AGA and 5 cases of TE. Diagnosis was made by correlation of clinical features and histological findings. AGA was defined by Terminal:Vellus < 4:1 while the ratio T:V >7 was in favour of TE. T:V values between 4:1 and 7:1 was interpreted as TE with early stages of AGA. Two patients diagnosed with TE with early stages of AGA had been suffering from diffuse hair shedding and thinning for more than 1 year. The remaining TE patients had presented with acute diffuse hair shedding which had started less than 6 months ago. AGA patients had a variable chronicity of 6-12 months. All specimens had been formaldehyde-fixed and embedded in
This article is protected by copyright. All rights reserved. paraffin wax. Limited horizontal sections had been cut, so that follicles from the level of the isthmus down could readily be found in each block (Fig. 1a). Normal scalp skin tissue (vertex) was obtained from patients who underwent routine scalp dermoid cyst resection. The excess skin around the cyst was cut into 5 mm × 5 mm squares, fixed in 10% neutral-buffered formaldehyde solution, and embedded in paraffin wax.
Histology
Horizontal (transverse) sections of 7 μm were cut from all specimens. Serial sections were evaluated at the level of the isthmus, from the sebaceous duct to the proximal-most attachment point of the APM (20-25 sections per biopsy). Sections were stained with Masson’s trichrome technique. Stained sections were photographed using an Olympus AX70 Provis microscope and an Optronics Camera.
Three dimensional reconstructions
One follicular unit consisting of 2-3 hairs was reconstructed from each biopsy, using “Reconstruct” software (developed by J. C. Fiala and K. M. Harris at Boston University, MA, USA18. Sections were aligned manually using four points of fixed structures (hair shaft centres and outer borders) in successive sections. Muscle and fat tissue volumes (from all follicles in a FU) were quantified using the same software.
Statistics
Statistical significance was evaluated using 1-tailed t-tests with unequal variances, using Excel 2010 software (Microsoft, Redmond, WA, U.S.A). P
