Hair Loss and Restoration

Jerry Shapiro, Nina Otberg

• Verlag: CRC Press
• Jahr: 2015
• ISBN:
  9780429586293
• Auflage: 2
• Thema: Medizin
• Thema: Medizinische Theorie, Praxis & Referenz

Treatment of hair disorders has progressed considerably over time. More patients are now interested in hair care and some are bombarded by promising advertisements. In reality, hair disorders may be complex and require accurate diagnosis for suitable treatment.Hair Loss and Restoration provides an extensive look at the practical management, both me

1 How to diagnose the patient with hair loss

Hair loss (alopecia) and scalp problems are very common complaints in the everyday dermatological clinic. Hair loss of any kind frequently causes major distress for the patient and can lead to anxiety and depression. Patients who suffer from hair loss and scalp problems often see several physicians and frequently report that they were not taken seriously, nobody looked at their scalp, and they got the advice to just live with their problem.

Even though we do not fully understand the pathophysiology of many hair diseases, there are always treatment options available. The patient needs to understand that the treatment of hair loss takes time and patience.

Hair basics

The entire scalp contains around 100,000 pigmented, terminal hair follicles. Blonds tend to have more, at 120,000, and redheads fewer, at 80,000 hair follicles [1,2]. There is ethnic variation, with an average density of 250–310 hairs/cm² in people of European decent [3, 4, 5, 6], approximately 150 hairs/cm² in African-American patients [6], and 120 hairs/ cm² in Asian patients [7]. In Europeans, hair shafts usually show an oval cross section; diameters can range from approximately 50 to 120 μm. Very fine hair with diameters less than 50 μm is most frequently seen in the Scandinavian population and northwestern Europe [8,9]. Hair of people originating from east Asia (China, Korea, and Japan) is usually referred to as oriental or Asian hair. It generally shows the greatest diameter, ranging from 100 to 130 μm [9]. Asian hair shafts are straight with no or very few twists along the shaft and with a round cross section [10, 11, 12]. The hair of people from sub-Saharan Africa is highly characteristic in shape. African hair is considerably flattened and grooved and frequently varies in diameter along one single shaft [13].

Every hair follicle undergoes an individual recurring cycle with growing and resting periods. The growing period (anagen) persists for 2–8 years, and the hair grows approximately 1 cm/month or 0.35 mm/day during this time. During the hair cycle, the middle and upper portions of the hair follicle are the permanent segment, whereas the lower portion is nonpermanent (Figure 1.1). The root (bulb area) of an anagen terminal follicle reaches deep into subcutaneous fat tissue. The anagen phase is followed by a transition period (catagen) of 2 weeks, during which the hair follicle undergoes programmed apoptosis. This transitional state is followed by a resting period (telogen) that lasts around 3 months. During telogen, the hair does not grow longer; the shaft is anchored in the mid-deep dermis.

Unlike most fur-bearing animals, where the hair cycle is synchronous, on the human scalp there is an asynchronous mixture of hairs actively growing and resting. In a healthy scalp, 80%–90% of hair follicles are in anagen [14]. A normal anagen to telogen ratio for the scalp hair is 9:1, although seasonal variations can be found [15,16]. The scalp sheds around 100 telogen hairs per day. Normal scalp skin also shows a variable number of small vellus hair follicles. Vellus hair follicles cover our entire body, except for palms and soles, with variable densities in different body sites. Vellus hairs are anchored in the mid-upper dermis; the hair shaft is free of color and less than 30 μm thick [17] (Figure 1.2).

Figure 1.1
During the hair cycle, the middle and upper portions of the hair follicle are the permanent segments of the hair follicle, whereas the lower portion is nonpermanent. (a) The growing or anagen hairs are anchored deeply within the subcutaneous fat and cannot be pulled out easily. The telogen hairs are located higher up in the dermis and can be pulled out relatively easily. The scalp consists of almost 90% hairs in anagen, 1% in catagen, and 10% in telogen. Anagen may last up to 2–6 years, telogen 3 months, and catagen 3 weeks. This ratio is usually uniformly distributed over the entire scalp. The dermal papilla (dp) is pulled upward with each cycle and during telogen is closely associated with the stem cells of the bulge area. Communication signals between dp and stem cells of the bulge probably determine the length of anagen and the matrix girth of the next hair cycle. (b) The newly formed anagen hair pushes out the previous telogen hair.

Figure 1.2
Vellus-like hairs are less than 0.03 mm in diameter and rarely grow more than 1–2 mm. Terminal hairs are coarse, over 0.06 mm in diameter, and can grow up to 1 m (3 ft).

Basic trichologic anatomy

To appreciate an organized protocol for alopecia, it is important to review the basics of hair anatomy. Hair follicles are skin appendages that are formed in week 16 of the early fetal period. They can be divided into four parts (Figures 1.3 and 1.4):

1. Infundibulum, extending from the follicular orifice to the sebaceous gland

2. Isthmus, extending from the sebaceous gland to insertion of the arrector pili muscle

3. Suprabulbar area, insertion of the arrector pili muscle to matrix

4. Bulb, consisting of the dermal papilla and matrix intermixed with melanocytes (Figure 1.5)

The lower portion of the follicle consists of five major portions: (1) the dermal papilla; (2) the matrix; (3) the hair shaft, from the inside to the outside of medulla, cortex, and cuticle; (4) the inner root sheath (IRS), consisting of the IRS cuticle, Huxley's layer on the inside and Henle's layer on the outside; and (5) the outer root sheath (ORS) (Figures 1.6 and 1.7). The base of the follicle is invaginated by the dermal papilla, which contains highly vascularized connective tissue. Dermal papilla fibroblasts are inherently different from nonfollicular fibroblasts. There is a large amount of acid-mucopolysaccharides within the dermal papilla, staining positively for Alcian Blue and metachromatically for toluidine blue. The ground substance consists of not only non-sulfated polysaccharides such as hyaluronic acid, but also sulfated mucopolysaccharides such as chondroitin sulfate. Increased activity of alkaline phosphatase can be found in the anagen phase.

The hair matrix has large vesicular nuclei and deeply basophilic cytoplasm. DOPA- positive melanocytes are interspersed between the basal cells of the matrix. Melanocytes are dendritic neural crest–derived cells that migrate into the epidermis in the first trimester. Melanin is a complex quinone-/indole–quinone-derived mixture of biopolymers produced in melanocytes from tyrosine [18]. Melanin is incorporated into the future cells of the hair shaft through phagocytosis of the distal portion of the dendritic melanocyte (Figure 1.8). Melanosomes of the hair follicle are larger than those of the epidermis. They lie singly or within groups not within lysosomes. They are located usually in the interfibrillary matrix, within the cells and only rarely in the intercellular space in the hair cortex. Two different types of melanin can be distinguished: eumelanin is brown or black, and pheomelanin, which results from the incorporation of cysteine, is yellow or red [19, 20, 21, 22, 23]. In eumelanin-containing follicles, melanocytes contain ellipsoidal melanosomes with lamellar internal structure (eumelano-somes). Pheomelanogenesis is associated with melanocyte-containing spherical melano-somes, which have a less well-defined internal structure containing granules and vesicles. Eumelaninogenic and phaeomelanogenic melanosomes can coexist in the same melanocyte but are produced in different pathways [24, 25, 26]. A preponderance of eumelanin is associated with brown or black hair and a preponderance of phaeomelanin with red or blond hair. The absence or relative absence of both melanin types results in white hair.

Figure 1.3
Diagrammatic representation of hair anatomy. The hair follicle is divided into four parts: bulb, suprabulbar area, isthmus, and infundibulum.

Figure 1.4
(a) Histology of the hair follicle on longitudinal section showing dermal papilla (DP), matrix (M), inner root sheath (IRS), outer root sheath (ORS), and fibrous root sheath (FRS). (b) Two anagen follicles side by side at the level of fat. Note the melanocytes within the matrix providing pigment to the hair. (Courtesy of Dr. Magdalena Martinka and Dr. David Shum.)

Figure 1.5
(a) Close-up of longitudinal section of dermal papilla (DP), which is an invagination of the dermis into the matrix (M). The DP allows capillaries to gain entrance to the cells of the matrix. It is the signal transduction and communication between the DP and the matrix that determines how long a hair will grow and how thick a shaft will be. Melanocytes fill the matrix and produce the pigment of the hair. (b) ...