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Classification of primary cicatricial (scarring) alopecias
In past years, several methods have been tried and tested
to properly classify the different forms of primary cicatricial
alopecias.
Some of these classification systems were based on the age of
onset, some on clinical features, some on pathological features,
etc. However, the most effective (as also the most popular)
of these classification systems is one developed and promoted
by
the North American Hair Research Society (NAHRS).
The categorization is based on the principal inflammatory cell
type involved in the scarring alopecia – lymphocytic and / or neutrophilic – that
is observed in scalp biopsy sections taken from active lesions.
Scarring alopecia conditions that do not show any specific traits
(analogous to those exhibited by lymphocytic or neutophilic types
of alopecias) are labeled non-specific or mixed infiltrates.
The classification system followed by the NAHRS group is inclusive
of the following:
1. Epidemiology (elements contributing to the occurrence or
non-occurrence of a disease in a population)
2. Pathophysiology of primary cicatricial alopecia
3. Clinical implications
Epidemiology
The occurrence of primary cicatricial alopecia in the general populace
is not fully understood. In this regard, in-depth studies of clinicopathologic
cases help better analyze the situation.
In the first survey conducted by Dr Whiting, patients (of ages
3-79 years) were evaluated for a period of nearly ten years. According
to this survey, the frequency of occurrence of scarring alopecia
was approximately 7.3%. It was further observed that the percentage
of women affected by primary cicatricial alopecia exceeded that
of men (with the female: male ratio being, 2.6:1). In another 5-year
retrospective study undertaken by Dr Tan and others, nearly 3.2%
of patients who underwent evaluation for hair disorders were found
to have primary scarring alopecias.
Though the two studies depicted disparity in the frequency of observed
cicatricial alopecia types, a lymphocytic infiltrate was identified
as the main causal factor in the majority of patients.
Pathophysiology of primary cicatricial alopecia
A close analysis of the basic anatomy (structure) and physiology
(the functions and processes) of the hair follicle gives a better
insight into the origin of primary cicatricial alopecia in human
beings.
The hair cycle comprises three phases – the anagen phase,
catagen phase and the telogen phase. The anagen phase is the active
phase of the hair follicle – a phase when the hair grows.
The catagen phase is a stage where the hair follicle stops producing
hair fiber, regresses and shrinks. The telogen phase is the resting
state of the hair follicle. The hair follicle then switches from
telogen back into a new anagen growth phase. During each hair cycle,
the lower part of the hair follicle (below the isthmus or site of
attachment of the arrector pili) goes through continued remodeling
and regeneration. This regenerative capacity of the hair follicle
is very much attributable to some slow-cycling yet potent cells
residing in the bulge area of the hair follicle. These stem cells
generate secondary germ cells or transit amplifying cells that migrate
in a bi-directional fashion and undergo synchronized differentiation
to:
(1) Restore and renew the upper follicle, including the sebaceous
gland and adjacent epidermis; and
(2) Re-grow the lower hair follicle during normal telogen to anagen cycling.
A deeper study of the anatomy and physiology of the hair follicle
reveals the Langerhans’ cells concentrated in the infundibular
epithelium, bulge and sebaceous epithelium, set off the initial
immune response to external and internal antigenic threats in hair
follicles. If the inflammation that results from the initial signals
of the Langerhans’ cells disrupts the stem cells in the bulge
region, scarring alopecia seems to develop.
Clinicial
implications
Histopathologic (the microscopic changes brought about in the tissues
by the disorder) examinations reveal that in most cases of primary
cicatricial alopecias the site initially affected is the upper portion
of the hair follicles that house the stem cells. The localization
or concentration of this inflammatory response to a particular site
may be caused by a wide variety of factors like exposure to ultraviolet
light (as in the case of patients detected with scalp DLE), certain
medicines (as in lichen planopilaris), bacterial infection (as in
folliculitis decalvans), etc.
Whatever be the initiating event, it is believed that the inflammation
either obliterates or permanently disrupts the functioning of the
critical elements that prompt follicular reconstitution by the stem
cells and cause permanent alopecia. The inflammation also destroys
the capacity for epidermal and sebaceous gland restoration, something
that explains the occurrence of epidermal and sebaceous gland atrophy
(or wasting away) in several types of primary cicatricial alopecias.
Differences between primary cicatricial alopecia types
Primary cicatricial alopecias are divided into lymphocytic, neutrophilic
and mixed types based on histopathological evidence of the predominant
inflammatory cellular infiltrate. The lymphocytic variants of cicatricial
alopecias exude clear, colorless liquid from the inflamed tissues,
whereas, the neutrophilic variants show neutrophilic accumulations
in and around otherwise normal scalp vessels. The mixed types on
the other hand, exhibit mixed characteristics of the both the above
scarring alopecias.
Studies proved that the ratio of incidence of lymphocytic and neutrophilic
cicatricial alopecias is 4:1. It has further been observed that
lymphocytic cicatricial alopecias usually affected middle-aged women,
whereas neutrophilic cicatricial alopecias were a more common disorder
in middle-aged men.
Differentiating between the various primary cicatricial alopecia
groupings (lymphocytic, neutrophilic, or mixed) has never posed
a big problem for the dermatologists and clinicians; the process
needed no more than standard microscopic analysis of skin biopsies.
The distinctive subtypes (both clinically and morphologically) of
primary cicatricial alopecia conditions, however, cannot be reliably
distinguished by such simple evaluation programs.
The analysis of the several variants of primary scarring alopecias
including;
(1) The lymphocytic scarring alopecias: discoid lupus erythematosus,
lichen planopilaris, frontal fibrosing alopecia, Graham Little syndrome,
pseudopelade of Brocq, central centrifugal cicatricial alopecia,
alopecia mucinosa, keratosis follicularis spinulosa decalvans;
(2) The neutrophilic scarring alopecias: folliculitis decalvans,
perifolliculitis capitis abscedens et suffodiens; and
(3) The mixed alopecias: folliculitis (acne) keloidalis, folliculitis
(acne) necrotica, erosive pustular dermatosis;
call for in-depth study – something that leads to exact diagnosis
identification and necessitates scalp examination and scalp biopsy.
Scalp
examination
Scalp examination involves viewing the scarred and adjacent hair-bearing
areas of the entire scalp with the help of a magnifying lens. Drawing
parallels to normal hair-bearing areas of the scalp help form an
idea of the pathologic condition. The concentration of symptoms
leads one to areas of active disease.
Follicular and interfollicular stigmata (a small mark, scar, opening,
etc.) in the form of atrophy, erythema (abnormal reddening of skin),
pigmentary alteration become all too apparent when viewed through
magnifying lens. Scalp examination also involves assessment of the
different alopecic patterns (central, patchy, reticulate, etc.).
These apart, evidence and extent of the extra-cranial infectivity
of the disease is also considered.
Scalp
biopsy
Scalp examination only suggests the probability of the existence
of a certain scarring alopecia condition. These diagnostic impressions
need to be confirmed through medical tests and microscopic examination
of a scalp biopsy. A scalp biopsy is taken from sites that have
clinically active disease and have tested positive for the hair
pull test. Sampling from end-stage areas of scarring alopecias does
not provide much pathologic information.
Classification of the various forms of primary scarring alopecias
require the following standard tests to be performed:
• Biopsy of a 4-mm diameter specimen skin sample collected
from a clinically active area of scarring disorder. Horizontal sections
give a complete view at multiple levels of most of the affected
hair follicles, hence transverse or horizontal sections are generally
preferred over vertical sections when only one biopsy is performed.
Thereafter, biopsy processing involves staining of transverse sections
with hematoxylin and eosin (H&E).
• Alternately, biopsy of two 4-mm diameter samples (one transverse
section and the other vertical) can be undertaken. Subjecting the
two sections to different tests, like the transverse section to
common histology tests and the vertical section to histology as
well as to direct immunofluorescence (DIF) tests, help evaluate
the condition better.
• Subjecting the specimens to various laboratory tests like
elastin, mucin and periodic acid-Schiff (PAS) stains are sure to
supply additional information for an even better analysis.
• Additional, optional biopsies from advanced areas of alopecia
probes into follicular and elastic tissue loss. The test also reviews
the pattern of elastic tissue loss and investigates the potential
for re-growth of the hair follicle.
The variants or subtypes of primary cicatricial alopecias exhibit
overlapping features when put through standard pathologic examination.
However, they display distinctive patterns of elastic tissue staining – differences
that have been attributed to disease-related differences in follicular
scar formation and also to the remodeling of the adventitial dermis
(the layer of skin lying below the epidermis and covering the follicle)
following follicular destruction.
Tests like DIF, VVG of biopsies or for that matter fluorescent
microscopic analysis of the stained sections help detect specific
tissue stain patterns – something that better appraise the
disorder and reinforce diagnostic precision.
Classification of primary cicatricial (scarring) alopecias references
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cicatricial alopecias. J Am Acad Dermatol. 2005 Jul;53(1):1-40.
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clinicopathology of 112 cases. J Am Acad Dermatol. 2004 Jan;50(1):25-32.
PMID: 14699361
- Wiedemeyer K, Schill WB, Loser C. Diseases on hair follicles
leading to hair loss part II: scarring alopecias. Skinmed. 2004
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- Sperling LC. Scarring alopecia and the dermatopathologist.
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