Physician Assistant CME : Derm Basics

Derm Basics

There are a few basic things that you need to know before you can start mastering dermatological conditions. The term lesion is used in dermatology as a general term for any sort of damage or defect found on the skin. There are two groups of skin lesions: primary and secondary. When you hear of a primary skin lesion think of it in terms of it being the first thing. In other words, a primary skin lesions would be something along the lines of a blister (bulla) that forms on the back of your heel after breaking in your new running shoes without the right socks on. When you hear of a secondary lesion think of it as being caused by something else. For example, remember that blister on your heal? Now it popped and as a result a crust has formed around the area. In this situation the bulla is the primary skin lesion because it came first and then the crust formed as a result so the crust is therefore a secondary skin lesion.

Some other things some other things you should brush up on before diving into dermatological conditions are some basic terms including:

Macule: a flat lesion on the skin < 1 cm in size. It can be pigmented but doesn’t have to be. They are entirely flat and cannot be felt, only seen. Ex: freckle
Patch: a macule that is > 1 cm. Ex: stork bite
Papule: Elevated, solid lesion with distinct borders < 1 cm. Ex: mole
Nodule: a papule that is > 1 cm. Ex: Lipoma
Vesicle: raised lesion < 0.5 cm and filled with serous fluid. Ex: chicken pox lesion
Bulla: raised lesion > 0.5 cm and filled with serous fluid. Ex: blister
Pustule: any sized lesion that is filled with pus. Ex: folliculitis
Plaque: elevated, superficial, flat, solid lesion that is > 1 cm. Ex: Psoriasis
Wheal: transient skin elevation that is solid, irregularly shaped, and has a variable diameter. Ex: mosquito bite
Petechiae: flat, < 0.3 cm lesion that does not blanch. Usually purple or red. Due to tiny hemorrhages in the dermis or submucosa. Ex: Rocky mountain spotted fever rash
Purpura: 0.3 cm – 1 cm lesion that does not blanch. Usually purple or red. Due to small bleeding into the skin. Ex: Henoch-Schonlein purpura
Ecchymosis: > 1 cm lesion that does not blanch. Usually purple or red. Due to bleeding into the skin. Ex: bruise
Crust: Hard or rough surface due to dried drainage (from blood, pus, or serum). Ex: Scab
Scale: thin flake of dead skin. Ex: psoriasis
Atrophy: thinning of the epidermis or subcutaneous fat which causes a depression in the skin. Ex: corticosteroid-induced dermal atrophy due to the prolonged application of topical corticosteroids
Tumor: Raised lesion or lesion that is palpable under the skin that is > 1 cm and is solid without any fluid. Ex: Xanthoma
Excoriation: damaged skin due to scratching. Usually linear or punctate. Ex: a scratched mosquito bite
Erosion: superficial open wound into the epidermis or mucosa (does not go into the dermis). Will not scar. Ex: Secondary lesion of herpes zoster
Ulcer: Deep open wound that goes into the dermis or subcutaneous tissue. May or may not be bleeding, will scar. Ex: diabetic foot ulcer
Fissure: Linear, open, and often painful crack in the skin. Ex: athlete’s foot
Lichenification: chronic thickening of the epidermis with exaggeration of its normal markings often due to scratching/rubbing. Ex: Chronic dermatitis
Cyst: Elevated, encapsulated lesion usually in a sac in the dermis or hypodermis that is filled with liquid or semisolid material. Ex: sebaceous cyst

Another important thing the know is the configuration of skin lesions:

Annular: ring-shaped with a central clearing
Arciform: arc-shaped lesion, an incomplete ring
Dermatomal: follows a dermatome (as seen with lesions of varicella zoster)
Discoid: disk-shaped lesion
Discrete: lesions tend to remain separate
Koebner phenomenon: appearance of lesions along site of injury
Linear: lesions follow a straight line
Grouped: cluster of lesions in a well circumscribed area
Guttate: individual lesions that look like spots or drops, almost as if someone took a dropper and dropped them on the skin
Nummular: coin-shaped lesion
Reticular: net like lesions
Serpiginous: lesions that wander as if following the path of a snake
Target lesions: series of concentric rings
Universalis: widespread lesions affecting the entire skin