Hair is a collective term for slender, threadlike
outgrowths of the epidermis of humans and forms a characteristic
body
covering. Every hair on the human body grows from a follicle,
a shaft
or opening on the surface of the skin. Although follicles
are most obvious on the scalp, they are also present everywhere
except on the palms, soles and mucous membranes.
The hair follicle is of great importance to the survival of
mammals. Hair fiber not only forms a tough barrier protecting
the epidermis from minor abrasions and/or from ultra violet
light, some hair follicles also have a highly developed nerve
network around them and provide sensory, tactile information
about the environment.
The pilosebaceous unit of the follicle is divided into three
parts, the infundibulum or the superficial part including
the sebaceous gland, the isthmus (middle segment) and the
inferior
part, which comprises the stem and the hair bulb deep in the
skin. Normally, the follicles carry out their functions with
few problems, but when they are damaged, or invaded by viruses,
bacteria and fungi, it can lead to an inflammatory reaction.
A limited inflammatory response focused on the superficial aspect
of the hair follicle is often termed a folliculitis. In order
to simplify the broad spectrum of the condition “folliculitis”,
the condition is classified into infectious folliculitis and
non-infectious folliculitis, based on clinical manifestations
and therapeutic applications. Non-infectious folliculitis can
be caused by the use of systemic and topical corticosteroids
and corticotrophin. These drugs can result in follicular skin
eruptions consisting of small, inflammatory pustules distributed
over the body. However, more commonly folliculitis is infectious
in nature. Depending on the causative agent, infectious folliculitis
is further classified as bacterial, syphilitic, fungal, viral
or parasitic.
For a practical approach to diagnosis of infectius
hair diseases, clinicians should have in-depth knowledge of
the different types
of infectious
agents and diseases they cause, their clinical presentations,
proper management and treatment measures. Good clinical and
pathological
correlation
may be required in some cases for successful evaluation, confident
diagnosis, and appropriate treatment application.
Clinical
evaluation
An evaluation of the clinical presentation, history, and physical examination
is very important in determining the cause of any hair disease.
A detailed personal history of the patient is essential
to determine the etiology. In order to classify a hair follicle
focused cutaneous eruption, a dermatologist should ask detailed
questions on the duration and temporal pattern of skin problems,
itching or pain, use of over-the-counter creams and even clothing
habits. When an underlying disease is suspected, a more detailed
history of related symptoms might be elicited. It is also
important to question the patient about predisposing factors
to cutaneous infections including drug abuse, any underlying
immune deficiency, exposure to possibly contaminated heated
water, and relations to food intake and exposure to sunlight.
The patient’s race, age, sex, occupation and the possibility
of other related dermatitis conditions is also helpful to
the diagnosis of hair follicle infection.
Pruritis or itching, defined as an unpleasant sensation
in the skin that provokes the desire to scratch, is a common
complaint in all the cases, and can represent a major diagnostic
and therapeutic challenge for practicing clinicians. Pruritis
can be localized or generalized, constant or intermittent,
mild or severe.
A thorough physical examination with particular attention to the location
and distribution of primary and secondary lesions as well as knowledge of
their evolution is crucial to the final diagnosis. Physical examination is
generally under bright light and it can involve the whole body. At this stage,
the doctor may apply Wood's light, which may aid in diagnosing types of mycosis,
or a dermatoscope, which makes the skin easier to see and may help differentiate
the lesions.
By applying their knowledge of primary and secondary lesions
and carefully evaluating the condition to determine the predominant
pattern, experienced dermatologists can arrive at the correct
diagnosis. A physical examination, which usually reveals the
typical lesions formed by follicular and perifollicular pustules,
papules and papulopustules, can supply evidence of any recognizable
disorder. Focal accumulations of pus (furuncles) or fluid
(vesicles, bullae) and scaling are indicative of the degree
of infection and corresponding inflammation of the hair follicle.
Dermatology has the benefit of having easy access to tissue (skin) for diagnosis,
and pathological examination of the skin lesions in some cases may help to
establish or substantiate the diagnosis made as a result of the clinical assessment.
Relevant investigations in the routine evaluation of bacterial infections
of the hair follicle include Gram stain smears of pus or exudates from the
lesions. Investigations also may include bacterial culture (to identify the
particular infective organism involved) coupled with antibiotic sensitivity
tests to help define the course of treatment. This can include nasal swabs
for those patients with recurrent skin infections.
Results of swabs and gram stain smears of the pustule content
can help verify diagnosis. Scrapings of flaky skin may also
be taken for fungal culture if a fungal infection is suspected.
A potassium hydroxide preparation may identify a yeast form
or candida. A positive Tzanck smear almost always indicates
a diagnosis of herpes simplex virus. Serological tests for HIV
or syphilis can be done when there is evidence or suspicion
of these predisposing factors. In some cases of viral folliculitis,
the diagnosis can be confirmed by sophisticated tests like polymerase
chain reaction. For more details on some of these tests, check
the “diagnosis / decisions” section of this web
site.
