Presentations
Approach to rash on the ward
The same eight steps, every presentation: threats first, then the history and exam that discriminate, one honest sentence, a mechanism-grouped differential, and the tests read in order.
Immediate threats
- A non-blanching rash with fever: meningococcal sepsis until proven otherwise
- Skin pain, blistering, mucosal involvement, Nikolsky sign: Stevens-Johnson syndrome, toxic epidermal necrolysis, staphylococcal scalded skin
- Urticaria with wheeze, stridor or hypotension: anaphylaxis
- Fever, facial edema, lymphadenopathy and eosinophilia weeks into a new drug: drug reaction with eosinophilia and systemic symptoms
- A rapidly spreading painful erythema out of proportion to the findings: necrotizing infection
History that discriminates
- Every drug started in the last eight weeks, with dates; the rash usually follows the drug by days to weeks
- Where it started and how it spread; itch versus pain; mucosal symptoms
- Fever, joint pain, sore throat, recent infection, sick contacts, travel
- Immune status, HIV, transplant, chemotherapy
- The patient's own dermatological history: eczema, psoriasis, previous drug reactions
Examination
- Undress the patient; examine the whole skin including the palms, soles, scalp, mouth, eyes and genitalia
- The blanching test with a glass; the Nikolsky sign where skin is tender
- Morphology: macule, papule, vesicle, pustule, wheal, purpura, target; the distribution
- Perfusion and the airway in any rash with fever or urticaria
- Lymph nodes, liver, spleen, joints
Problem representation
A symmetric morbilliform eruption starting on the trunk nine days into a new antibiotic in a well patient (a simple drug exanthem) versus a painful dusky eruption with mucosal erosions and a positive Nikolsky sign two weeks into an anticonvulsant (an emergency).
Differential, by mechanism
Drug
- Morbilliform exanthem
- Urticaria
- Fixed drug eruption
- Stevens-Johnson syndrome and toxic epidermal necrolysis
- Drug reaction with eosinophilia and systemic symptoms
- Acute generalized exanthematous pustulosis
Infection
- Viral exanthems
- Meningococcemia
- Cellulitis and necrotizing fasciitis
- Staphylococcal and streptococcal toxin syndromes
- Herpes zoster
- Secondary syphilis
Vascular and systemic
- Vasculitis and palpable purpura
- Thrombocytopenic purpura
- Lupus
- Dermatomyositis
- Erythema multiforme and erythema nodosum
Ward-acquired
- Contact dermatitis to tape or antiseptic
- Miliaria
- Scabies
- Pressure and moisture injury
Investigations
- None for a simple drug exanthem beyond stopping the drug; the diagnosis is clinical
- Full count with eosinophils, liver and renal panel when a systemic drug reaction is possible
- Blood cultures and immediate antibiotics for a non-blanching rash with fever; a skin swab and biopsy where the morphology is unclear
- Serology for syphilis and HIV where the story fits; a viral swab of a vesicle
Interpretation
- Timing against the drug chart is the single most useful piece of data
- Mucosal involvement and skin pain move a rash from clinic to emergency
- Eosinophilia with a rash and a fever is a systemic drug reaction until proven otherwise
Next steps
- Stop the suspect drug and write the reaction in the record and the allergy list, with the type
- Refer the emergencies today: mucosal disease, blistering, purpura with fever, the toxin syndromes
- The morphology and the rest of dermatology live in DermSpace; the sick patient with a rash lives here
Connected
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