⌘K
Volume 13

A study guide to dermatology.

For the rash that shows up between rounds, the drug chart that needs revisiting, and the patients whose skin speaks first. Last revised 2026.

05 topics

Dermatology

Anaphylaxis · Drug Reactions · Nutrition · Systemic Signs · Inflammatory

01

Anaphylaxis

▾
Clinical Picture

Pruritus · flushing · hives · conjunctival pruritus · angioedema · dyspnea · stridor · hypoxemia · wheeze · vomiting · diarrhea · cramping abdominal pain · hypotension · syncope · incontinence.

Mechanism: IgE · mast cells.

Triggers: foods · medications · insect stings · radiocontrast media · perioperative agents · exercise · seminal fluid · idiopathic.

Epinephrine first, every time. Antihistamines and steroids do not treat the airway or the shock — they are adjuncts. The pause to reach for them is where people die.
Epinephrine · Dosing
IM is the default · IV only when refractory or arresting
IM (default). Epinephrine 0.01 mg/kg IM (max 0.5 mg) · repeat q5–15 min PRN · 1:1000 = 1 mg/mL
IV (refractory). Epinephrine 0.05–0.1 mg IV over 5 min · infuse 2–10 mcg/min titrated to BP · 1:10,000 = 0.1 mg/mL
Adjuncts

Inhaled SABA · antihistamines · supplemental O₂ · IV crystalloid fluids · vasopressors · corticosteroids.

Discharge

Observation ≥12h · prescribe self-administered epinephrine auto-injector at discharge.

02

Cutaneous Drug Reactions

▾

The Big Four · Severity Spectrum

Read by onset · skin signs · systemic features

ReactionOnsetSkin findingsSystemic / LabsTreatment
Exanthematous
(morbilliform)		 72 h – 10 d after drug · fades over 1–3 weeks Pruritic macules / papules on trunk & proximal extremities Fever · pruritus Symptomatic: anti-H1 + topical corticosteroid
DRESS 2–8 weeks after drug · lasts >15 days Morbilliform rash trunk → distally · pustules · facial edema Arthralgia · fever · eosinophilia · lymphadenopathy · hepatitis. RegiSCAR score for diagnosis / prognosis. Oral corticosteroids ± IVIG
SJS / TEN 1–4 weeks after drug · lasts weeks – months Prodromal URTI · bullae · mucous membrane ulcerations · conjunctivitis · skin detachment · trunk / face. SJS <10% · SJS-TEN 10–30% · TEN >30% BSA Critical illness ICU / burn unit · supportive · corticosteroids · cyclosporine · infliximab · etanercept
AGEP Rapid onset Widespread pustules · erythema Fever · leukocytosis · eosinophilia Self-limiting (~2 weeks)
Erythema Multiforme

Target lesions on extremities ± mucosal erosions.

Triggers: recurrent HSV infection · drug allergy (sulfonamides · penicillin · phenytoin) · Mycoplasma infection.

Treatment: stop offending agent · treat underlying cause.

Fixed Drug Eruption

Discrete round / oval lesions that recur in the same spot with every re-exposure to the offending drug.

Erythema Nodosum

Tender subcutaneous nodules on the lower legs · prodromal fever · malaise · arthralgia.

See Topic 05 for the full differential and treatment.

Urticaria

Pruritic erythematous wheals · transient <48 h.

Acute <6 weeks · chronic ≥6 weeks.

Triggers: infections · food · drugs · venom · physical (cold · dermatographism · delayed pressure · solar · water · contact).

Chronic Spontaneous Urticaria · Workup & Ladder
Hived most days · >6 weeks · no clear trigger · ± angioedema
Workup. CBC · ESR · CRP · TSH / TPO antibody · mast cell tryptase · biopsy · total IgE
1. Daily antihistamine
2. Refractory › omalizumab
3. Refractory › cyclosporine
03

Nutritional Disorders of the Skin

▾

Deficiency → Skin Findings

Recognize the deficiency at the bedside

DeficiencySkin / Mucosal findingsSystemic clues
Vitamin C
(scurvy)		 Perifollicular hemorrhage · follicular hyperkeratotic papules · coiled "corkscrew" hairs · petechiae · purpura · splinter hemorrhages Gingival bleeding
Niacin
(pellagra)		 Erythema in sun-exposed areas · scaling hyperpigmented rash Diarrhea · insomnia · dementia
Vitamin A Conjunctival / generalized xerosis · follicular hyperkeratotic papules on extensor surfaces (toad skin) · corneal scarring Bitot spots · night blindness
Vitamin B2
(riboflavin)		 Oral-ocular-genital syndrome · angular stomatitis · glossitis · pruritic scrotal dermatitis · balanitis · seborrheic dermatitis —
Vitamin K Ecchymosis Coagulopathy
Zinc Perioral / perianal dermatitis · vesicles / pustules / plaques on erythematous base CLD · IBD as common contexts
04

Dermatologic Signs of Systemic Disease

▾

Skin Sign → Underlying Disease

The pattern recognition table

SignUnderlying disease
Heliotrope rash Dermatomyositis
Mechanic's hands Dermatomyositis / antisynthetase syndrome
Xanthomas Familial hypercholesterolemia
Acanthosis nigricans T2DM
Pyoderma gangrenosum IBD · inflammatory arthritis · lymphoproliferative disorders
Dermatitis herpetiformis Celiac disease
Erythema nodosum IBD · TB · sarcoidosis · coccidioidomycosis · streptococcal infection · Löfgren syndrome (bilateral hilar lymphadenopathy + erythema nodosum + lower extremity arthralgia) · drug reaction
Severe seborrheic dermatitis / psoriasis HIV
Porphyria cutanea tarda · lichen planus HCV
The skin is often the first chart you read. Acanthosis on the neck before the HbA1c comes back; Löfgren on the legs before the chest X-ray; mechanic's hands before the CK is drawn.
05

Inflammatory Dermatoses

▾
Psoriasis · Clinical Picture

Erythema · scaling · induration on extensor surfaces · scalp · ears · intertriginous folds · genitalia. Nail pitting / thickening / yellowing. 30% develop psoriatic arthritis.

Triggers: systemic glucocorticoids · lithium · antimalarial drugs · tetracyclines · BBs · NSAIDs · ACEi.

Variant
Guttate Psoriasis

Many small drop-like papules / plaques on the trunk, preceded by β-hemolytic Strep infection.

Variant
Pustular Psoriasis

Abrupt onset · generalized erythema · lakes of pus, often preceded by abrupt discontinuation of glucocorticoids.

Emergency
Erythroderma

Redness / scaling 80–90% BSA · abrupt glucocorticoid discontinuation › risk of infection · electrolyte abnormalities.

Psoriasis · Treatment Ladder

Smoking cessation across all severities.

Localized › topical vitamin D analogues ± topical glucocorticoids.

Systemic therapy indications: skin involvement >10% · psoriatic arthritis · resistant disease.

Systemic options: phototherapy · methotrexate · TNFα inhibitors · IL-17 inhibitors · IL-12 ± 23 inhibitors.

Erythema Multiforme

Target lesions on extremities ± mucosal erosions.

Triggers: recurrent HSV · drug allergy (sulfonamides · penicillin · phenytoin) · Mycoplasma infection.

Treatment: stop offending agent · treat underlying cause.

Erythema Nodosum

Tender bilateral dermal red nodules on the shins — a panniculitis.

Causes: IBD · TB · sarcoidosis · coccidioidomycosis · streptococcal infection · Löfgren syndrome (bilateral hilar lymphadenopathy + erythema nodosum + lower extremity arthralgia) · drug allergy · OCP · HRT.

Course: self-limiting 4–6 weeks.

Treatment: NSAIDs · compression stockings.

Sweet Syndrome

Painful · edematous red papules / plaques on the face, neck, extremities · high fevers · leukocytosis · elevated inflammatory markers · muscle / joint pain · preceding GI / URT infection.

Histology: biopsy › neutrophilic dermal infiltration.

Associations: AML · Behçet · CML / CLL · IBD · MM · myelodysplastic syndrome · myeloproliferative disorders · relapsing polychondritis · RA · solid tumors · thyroid disease.