5.2 Dermatologic
Key Takeaways
- Dermatologic content is approximately 5% of the PANRE, about 12 items on a 240-question exam, and emphasizes pattern recognition and morphology.
- Atopic dermatitis (eczema) is a pruritic, relapsing disease managed with emollients and topical corticosteroids; psoriasis classically shows well-demarcated plaques with silvery scale on extensor surfaces.
- The ABCDE rule (Asymmetry, Border irregularity, Color variation, Diameter over 6 mm, Evolution) screens pigmented lesions for melanoma, the deadliest common skin cancer.
- Basal cell carcinoma is the most common skin cancer and rarely metastasizes; squamous cell carcinoma can metastasize, and both are strongly linked to ultraviolet exposure.
- Stevens-Johnson syndrome and toxic epidermal necrolysis are severe drug eruptions with mucosal involvement and skin detachment; immediate drug discontinuation and supportive care are essential.
Why This Section Matters
The NCCPA PANRE blueprint allocates roughly 5% to the Dermatologic System, about 12 items on a 240-question exam. Dermatology items reward accurate morphologic description and the ability to separate benign rashes from malignancy or a life-threatening drug reaction.
Describing Lesions
Using consistent terminology is the foundation of dermatologic reasoning and a common item theme.
| Term | Definition |
|---|---|
| Macule | Flat, non-palpable color change less than 1 cm |
| Patch | Flat color change 1 cm or larger |
| Papule | Raised, palpable lesion less than 1 cm |
| Plaque | Raised, flat-topped lesion 1 cm or larger |
| Vesicle / Bulla | Fluid-filled lesion (small / large) |
| Pustule | Pus-filled lesion |
| Nodule | Raised, solid lesion extending into the dermis |
| Wheal | Transient, edematous, pruritic plaque (urticaria) |
Also note configuration (annular, linear, grouped), distribution (flexural vs. extensor, photo-distributed, dermatomal), and secondary changes (scale, crust, lichenification, excoriation).
Common Inflammatory Dermatoses
Atopic Dermatitis (Eczema)
Atopic dermatitis is a chronic, relapsing, intensely pruritic disease often associated with the atopic triad (atopic dermatitis, asthma, allergic rhinitis). In infants it favors the face and extensor surfaces; in older children and adults it favors flexural areas (antecubital and popliteal fossae). Management centers on liberal emollients, trigger avoidance, and topical corticosteroids for flares, with topical calcineurin inhibitors as steroid-sparing options.
Psoriasis
Psoriasis classically presents with well-demarcated, erythematous plaques topped by silvery scale on extensor surfaces (elbows, knees), the scalp, and the lumbosacral area. Nail pitting and a subset with psoriatic arthritis may occur. Limited disease is treated with topical corticosteroids and vitamin D analogues; extensive disease may require phototherapy or systemic agents.
Acne Vulgaris
Acne vulgaris results from follicular hyperkeratinization, sebum, Cutibacterium acnes, and inflammation, producing comedones, papules, pustules, and in severe cases nodules. A common item theme is stepwise therapy: topical retinoids and benzoyl peroxide for comedonal/mild disease, adding topical or oral antibiotics for moderate inflammatory disease, and reserving systemic isotretinoin for severe nodulocystic or treatment-resistant acne with appropriate monitoring.
Skin and Soft-Tissue Infections
| Condition | Key Features |
|---|---|
| Impetigo | Honey-colored crusts, often perioral, contagious; superficial bacterial infection |
| Cellulitis | Spreading, warm, tender erythema with indistinct borders; usually streptococci or staphylococci |
| Erysipelas | Sharply demarcated, raised, fiery-red plaque, often facial; superficial cellulitis variant |
| Abscess | Fluctuant, walled-off collection; incision and drainage is the key intervention |
| Tinea (dermatophyte) | Annular, scaly, advancing border with central clearing; KOH prep shows hyphae |
| Herpes zoster | Painful grouped vesicles in a single dermatome that does not cross midline |
| Necrotizing fasciitis | Pain out of proportion, rapid progression, systemic toxicity — a surgical emergency |
KOH = potassium hydroxide. The exam-critical discriminator is recognizing necrotizing fasciitis and other rapidly progressive infections that require urgent surgical evaluation rather than oral antibiotics alone.
Skin Cancer Recognition
Ultraviolet exposure is the dominant modifiable risk factor for the major skin cancers.
- Basal cell carcinoma (BCC): the most common skin cancer. A pearly, telangiectatic papule that may ulcerate ("rodent ulcer"); locally invasive but rarely metastasizes.
- Squamous cell carcinoma (SCC): a firm, scaly, or ulcerated lesion on sun-exposed skin, often arising from actinic keratoses; can metastasize, especially on the lip or ear or in immunosuppressed patients.
- Melanoma: the most lethal common skin cancer. Screen pigmented lesions with the ABCDE rule.
| ABCDE | Concerning Feature |
|---|---|
| A — Asymmetry | One half unlike the other |
| B — Border | Irregular, notched, or poorly defined |
| C — Color | Variegation or multiple colors |
| D — Diameter | Greater than 6 mm (about a pencil eraser) |
| E — Evolution | Change in size, shape, color, or new symptoms |
Any lesion suspicious for melanoma warrants biopsy; prognosis correlates strongly with tumor (Breslow) depth, which is why early recognition is emphasized on the exam.
Drug Eruptions
Most drug eruptions are benign morbilliform (maculopapular) rashes. The exam priority is recognizing severe cutaneous adverse reactions:
- Stevens-Johnson syndrome (SJS) / toxic epidermal necrolysis (TEN): painful skin with mucosal involvement, blistering, and epidermal detachment (Nikolsky sign); SJS and TEN are distinguished by the percentage of body surface area detached. Stop the offending drug immediately and provide intensive supportive care.
- Drug reaction with eosinophilia and systemic symptoms (DRESS): rash with fever, facial edema, eosinophilia, and internal organ involvement; onset is typically delayed weeks after starting the drug.
- Urticaria/angioedema with anaphylaxis: wheals with airway or hemodynamic compromise require immediate intramuscular epinephrine.
Widespread skin pain, mucosal lesions, or blistering after a new medication should prompt urgent discontinuation and escalation rather than symptomatic outpatient treatment.
A 19-year-old started a new antibiotic 10 days ago and now has fever, painful skin, oral and conjunctival erosions, and blistering with a positive Nikolsky sign over part of the body. Which is the most appropriate immediate action?
A 67-year-old with extensive sun exposure has a slowly enlarging pearly papule with central ulceration and visible telangiectasias on the nose. Which lesion is most likely?
Which lesion description best matches the classic appearance of plaque psoriasis?