Dermatologic System
The dermatologic domain tests skin infections, inflammatory dermatoses, drug eruptions, and skin cancer, emphasizing pattern recognition and recognition of necrotizing emergencies.
Core rules
- Cellulitis is a spreading, warm, tender, erythematous plaque without fluctuance. Cover streptococci and staphylococci, commonly with cephalexin. Mark the border and reassess.
- Abscess requires incision and drainage; antibiotics are adjunctive for systemic symptoms, extensive disease, or immunosuppression.
- Atopic dermatitis: emollients plus topical corticosteroids; use the lowest effective potency and step up for flares. Avoid oral antibiotics unless there is clear secondary infection.
- Melanoma: assess ABCD-asymmetry, border irregularity, color variation, diameter over 6 mm-and evolving lesions. Any suspicious lesion needs biopsy, not reassurance.
Worked example
A 50-year-old man has a warm, red, tender left leg without fluctuance or drainage. This is cellulitis. He is afebrile and systemically well, so start oral cephalexin and mark the border. If there is a fluctuant abscess, drain it rather than relying on antibiotics alone.
Traps
- Missing necrotizing fasciitis when pain is out of proportion and the patient is toxic.
- Treating stasis dermatitis with antibiotics.
- Failing to drain an abscess.
- Biopsying suspected melanoma with a superficial shave instead of an adequate specimen.