DERMATOLOGY REVIEW

Structure and Physiology of Skin, Hair, Nails

  1. Schwartz, M. H. Textbook of Physical Diagnosis, Chapter 5, The Skin
  2. Marieb, E.N. & Mallatt, J. Human Anatomy, Chapter 5, The Integumentary System, pp 100-110.

 

I. Layers of the skin:

  1. Epidermis
  1. Keratinized, stratified squamous epithelium
  2. Main cell type is keratinocyte - gives epidermis its protective properties.
  3. Stratum basale – deepest layer – cells germinate for growth & renewal of epidermis – melanocytes & sensory Merkel cells are here
  4. Stratum spinosum – Langerhans cells – help activate immune system
  5. Stratum granulosum – cells secrete waterproofing substance into extracellular space to slow water loss
  6. Stratum Lucidum – thin, clear layer which occurs only in thick skin, e.g., soles of feet
  7. Stratum Corneum – most external part of epidermis Flat dead cells, protect skin from abrasion & penetration, prevents water loss dead cells shed as skin flakes & dandruff

B. Dermis

  1. Strong, flexible connective tissue
  2. Contains blood vessels, nerves, glands & hair follicles
  3. Reticular layer is deepest – 80% of dermis – dense connective tissue – gives strength & resilience to skin – elastic fibers provide stretch & recoil properties – extreme stretching related obesity or pregnancy tear dermis resulting in striae ("stretch marks")
  4. Papillary layer – superficial 20% -- indent into epidermis – result in dermal ridges which give hands & feet their gripping ability – responsible for fingerprints.

C. Hypodermis

  1. Below the dermal layer
  2. Also called superficial fascia
  3. Consists primarily of adipose tissue
  4. Stores fat & provides an insulating layer which thickens with weight gain: men in abdomen, women in thighs & breasts first.
  5. Anchors skin to underlying muscle & other structures and absorbs & deflects blows.

D. Skin Color

  1. Varies according to amount of melanin & carotene pigments and oxygenation level of hemoglobin.
  2. Melanin protects keratinocytes from damaging effects of sun’s UV radiation.
  3. Epidermis also produces vitamin D when stimulated by UV radiation

II. Appendages of the Skin

A. Hair & Hair Follicles

B. Sebaceous Glands

C. Sweat Glands

  1. Eccrine – secrete sweat which evaporates to cool the skin & body
  2. Apocrine – mostly in axillary, anal, & genital areas – Contain fatty acids – bacterial action causes odor – may function as scent glands

D. Nails – Scale-like modification of epidermis.

 

  1. Developmental Changes
  1. Fetus has downy lanugo coat which decreases the closer to term it reaches
  2. Fetal sebaceous glands produce vernix caseosa – protects skin in utero
  3. Melanocytes change with UV’s damaging rays – gives rise to Melanoma.
  4. Epithelial cells change with UV exposure – leathery look, Squamous cell carcinoma
  5. Basal Cell carcinoma results from changes in the basal layer cells 2o UV exposure.
  6. In elderly, replacement rate for epidermal cells slows, skin & hair thin. Skin glands are less active, Decreased elastin fibers & subcutaneous fat result in wrinkles.

IV. Assessment of the Skin

A. Subjective

  1. Most of assessment is subjective – a good history is paramount to accurate diagnosis
  2. Characteristics of lesion(s): When did it start?, Has it changed or spread?, Does it itch or burn?, Reaction to sunlight?
  3. What treatment have you tried?
  4. Are there any related symptoms (joint pain, fever, fatigue, etc)
  5. Any recent travel?
  6. History or symptoms of allergies
  7. Any chronic diseases? (autoimmune, malignancies, endocrine)
  8. What medications are you taking? Any recent changes?
  9. Any recent change in soaps, cosmetics
  10. Occupational exposure?
  11. Life stresses?
  12. Household or recreational exposure to chemicals or natural substances? (Check for hobbies)
  13. ETOH, Tobacco, or other substance use?
  14. Family history of skin diseases? (atophy, allergy, psoriasis, etc)
  15. Ever had this type of rash before?
  16. What does patient think cause is?

B. Objective

  1. Where are lesions located?
  2. Primary features: What do lesions look like? (configuration, symmetry)
  3. Secondary features: Crust, erythema, excoriation, pigment change
  4. Distinguishing features: Size, Systemic or Lab findings

C. Assessment/Analysis

Is diagnosis firm or undetermined

D. Plan

  1. Document treatment
  2. Document medications prescribed
  3. Follow-up
  4. Client education

V. Terminology

Note: Please review Habif, pp. 1 - 24.

A. Primary Lesion: Initial skin changes uninfluenced by infection, trauma, or therapy.

  1. Macule: Circumscribed spot, different in color from surrounding skin, flat with skin surface. (e.g., Freckle, Viral Exanthem, Mongolian spot, Vitiligo)
  2. Papule: Circumscribed solid elevation on skin 0.5 cm or less (e.g., Nevi, Warts, Acne, Melanoma)
  3. Plaque: Circumscribed solid superficial elevation on skin > 0.5 cm. (e.g., Eczema, Psoriasis, Tinea corporis)
  4. Nodule: Circumscribed solid elevation on skin > 0.5 cm. (e.g., Basal cell carcinoma, Hemangioma). Note: A Large nodule is called a tumor.
  5. Pustule: Small circumscribed skin elevation containing purulent material (e.g., Chicken pox, Impetigo, Herpes Zoster, Acne).
  6. Vesicle: Circumscribed skin blister 0.5 cm or less which contains serous fluid (e.g., Chicken pox, Eczema, Scabies)
  7. Bulla: Circumscribed skin blister > 0.5 cm which contains serous fluid (e.g., Lupus, Pemphigus).
  8. Wheal: Irregular elevated edematous plaque which results from infiltration of dermis with fluid. Transitory in size & shape. (e.g., Hives, Angioedema)

B. Secondary Lesion: Changes which occur as a result of progression of disease, infection, or scratching.

  1. Scales: Superficial excess dead epidermal cells (e.g., Psoriasis, Scarlet fever, Seborrheic dermatitis, Xerosis)
  2. Crust: Dried exudate - serum & cellular debris - scab (e.g., Impetigo, Tinea capitis)
  3. Erosion: Focal loss of epidermis - heals without scarring (e.g., Candidiasis, senile skin)
  4. Ulcer: Focal loss extending into dermis - may scar (e.g., Chancroid, Decubitus, Stasis ulcer)
  5. Fissure: Deep skin split into dermis - sharply defined (e.g., chapped hands, Eczema)
  6. Atrophy: Depression in skin due to skin thinning (e.g., Aging, Discoid Lupus, Striae)
  7. Scar: Abnormal fibrous tissue which replaces normal tissue after skin injury (e.g., Burns, Acne, Chicken Pox)

C. Special Lesion: Unique change which does not meet properties of Primary or Secondary Lesions.

  1. Excoriation: Superficial linear erosion caused by scratching
  2. Cyst: Enclosed cavity with membranous lining - may contain liquid or semisolid matter
  3. Milia: Small, superficial cyst of keratin with no visible opening
  4. Burrow: Narrow, elevated channel caused by parasite
  5. Lichenification: Increased skin markings with thickened epidermis caused by scratching - washboard appearance
  6. Petechiae: Circumscribed deposit of blood < 0.5 cm (e.g., Meningococcemia)
  7. Purpura: Circumscribed deposit of blood > 0.5 cm (e.g., Rocky Mountain Spotted Fever, Platelet abnormalities, Senile purpura)
  8. Telangiectasia: Dilated superficial blood vessels (e.g., Basal cell carcinoma, Lupus, Vascular spiders of pregnancy or cirrhosis)

D. Distribution: Where lesions are found on the body

  1. Most skin diseases have preferred regions of the body for involvement
  2. Some diseases have a photodistribution (preference for regions of the body exposed to the sun), e.g., Lupus, Photodrug eruption
  3. Some disease will follow dermatome distribution (e.g., Herpes zoster)
  4. Some diseases will occur almost anywhere on the body (e.g., Contact dermatitis, Herpes Zoster)

E. Distinguishing Characteristics: Epidemiology, size, related symptoms, or laboratory results

  1. Epidemiologic characteristics most significant include age, region of country, household or work environment, recreational activities.
  2. Examples of related symptoms include erythema, lymphadenopathy, respiratory symptoms, musculoskeletal pain or swelling, fever, edema, etc.
  3. Common examples of lab tests include, KOH prep, Skin scrapings, Gram stain, Bacterial cultures, Cytology, Wood's light examination, Biopsy, and blood tests (e.g., ANA, titers)