Background
- Acute IV [cell mediated] hypersensitivity rxn
- 10/7 post drug/bug/other trigger
- Varies from mild rash to life threatening SJS-TEN
- Precipitating factors include HSV, EBV, medications
- May recur with repeated trigger (e.g. recurrent HSV)
- M>F
- Occasionally post vaccine (BCG, polio, Tdap)
- N.B. ±mucous membrane involvement
Triggers
Almost anything but common are:
Viral:
- HSV, CMV, EBV, Hep (all), VZV
Bacterial
- Strep, Mycoplasma P
Drugs
- Sulfa/penicillin based
- Anticonvulsants
Clinical
Symptoms
- Prodromal "URTI" → (day 3+) non-itchy rash
- Peripheral (incl. palms/soles) ache/rash spreads centrally
- ± mucous memb. (eyes, mouth, genital)
- Heal (no scar, possible ↑/↓ pigmentation) after 7 days
Signs
- ±SIRS (beware SJS-TEN)
- Papules → tender target lesions
- Dull-red macule, central vesicle/bulla
- Target lesions (enflamed edges)
- Nikolsky's negative (rub ≠ shear upper dermal layers)
Differential Dx
- Septicaemia (incl. meningococcal/nec. fasc.)
- Herpes simplex virus (HSV)
- Mycoplasma pneumoniae (±CXR)
- Burns (chemical etc
- Pemphigoid (beware elderly)
- Vasculitis (tender infarcted "bruises") e.g SLE
- Erythroderma (usually very unwell)
- Viral exanthems (commonest in children)
Investigations
Only if clinically indicated:
- Clinical Dx so only Ix if clinically unwell (? SJS-TEN)
- ± CXR (pneumonia)
Management
- Stop trigger if possible
- Analgesia, explanation
- Antihistamines
- ±mouth wash
- Consider po antivirals in (well) HSV