Rash

• Rash history

  Much of the diagnosis comes from examining the rash or lesion itself, but history taking is still important.

  History of presenting complaint

  Features of the rash:

  • Evolution of rash/lesion over time.
  • Onset at multiple sites and/or symmetrical? Suggests an internal cause.
  • Does sun exposure make it worse (e.g. SLE) or better (e.g. psoriasis)?

  Associated symptoms:

  • Itch (common) and pain (uncommon), both of which can be explored with SOCRATES.
  • Ooze or weeping? Suggests eczema.
  • Loosing sleep from discomfort?

  Possible causes:

  • Contact with substances at work or as part of a hobby. May cause allergic or irritant contact dermatitis.
  • Medications.

  Sun exposure history if you suspect cancer:

  • Do you tan/burn often?
  • Sunbed use.
  • Lived abroad?
  • Worked outside?

  Past medical history

  • Previous skin diseases.
  • Personal or family history of atopy, eczema, or psoriasis.
  • Any friends/family with an itchy rash? May suggest infectious cause such as scabies.

• Examining and describing a rash

  Level

  • If problem is in the dermis, the skin stays smooth.
  • If in the epidermis, it won't.

  Surface features

  Crust (aka scab):

  • Orange-yellow bits of dry serum, pus, and/or blood.
  • Other lesions – rash, lump, ulcer – might lie underneath, so crust should be removed to check.

  Scale (aka hyperkeratosis):

  • White-yellow flakes from a thickened stratum corneum (upper layer of epidermis) in which keratin has accumulated.
  • Most commonly seen in psoriasis.
  • May co-occur with crust.

  Thickness

  Thickening:

  • Scale
  • Lichenification: thickened epidermis with exaggerated skin lines. Caused by constant scratching or rubbing.
  • Scarring: suggests damage to dermis. Can be hypertrophic – as in normal scarring or keloid scarring – or atrophic – post-acne or with steroid use.

  Thinning/absences of skin layers:

  • Ulcer: full break (all the way through) of at least the epidermis. While healing it may feature exudate or crust (orange-yellow), pus (thick yellow), or necrotic tissue. Leave a scar.
  • Erosion: partial break, which heals without leaving a scar.
  • Excoriations: lots of small erosions which are self-inflicted from scratching.

  Factors affecting colour

  Melanin:

  • Primary determinant of skin colour, from albino to black.
  • Eumelanin: appears dark brown if superficial, but blue if deep.
  • Phaeomelanin: gives a pink-red colour to skin, and red hair.

  Blood:

  • Pink, suggesting ↑O2.
  • Dusky purple, suggesting ↓O2. If it is non-blanching, this suggests capillary leak e.g. vasculitis, sepsis.

  Necrosis:

  • Green, yellow, and/or black.
  • This gunk is known as 'slough' (pronounced 'sluff').

  Haemosiderin deposition:

  • Yellow-brown.
  • Causes: varicose eczema, haemochromatosis.

  Geography

  Borders:

  • Rolled: BCC.
  • Well-demarcated: psoriasis.

  Distribution:

  • Symmetry: internal/systemic cause.
  • Extensor/flexor.
  • Contact sensitivity e.g. on finger tips.
  • Sun-exposed.
  • Linear grouped papules: insect bites.
  • Mid-back spared: self-inflicted.

  Summarize findings

  “On the { location }, there is a { widespread / localised / [a]symmetrical }, { erythematous / brown } { lesion / area / area of discrete lesion sites }, covering approximately { X x Y cm }. It is { well / poorly } demarcated, and contains { macules / papules / patches / nodules / pustules / vesicles / blisters }.”

  Mnemonic

  6S + 3B:

  • Scabby
  • Scaly
  • Scrunched i.e. lichenification
  • Split: ulcer, erosion, excoriation
  • Scarred
  • Smooth: suggests a problem in the dermis as surface is unaffected.

  Colour:

  • Blood (including subcutaneously): erythematous, pink, purple.
  • Black: necrosis, may also be green and yellow.
  • Brown: melanin, haemosiderin.

• Skin lesion types

  The threshold between small and large lesions can be 5 mm (used below) or 1 cm.

  Flat lesions

  • Macule: small, flat, change in colour.
  • Patch: large (>5 mm), flat, change in colour.

  Raised lesions

  • Papule: small, raised lesion.
  • Nodule: large (>5 mm), raised lesion.
  • Plaque: flat-topped raised area, >5 mm, a broad or plateau-like nodule.

  Fluid-filled lesions

  • Vesicle: <5 mm
  • Bulla: >5 mm
  • Blister: generic term for vesicles and bullae.
  • Pustule: pus-filled.
  • Cyst: cavity / closed sac, lined with epithelium, distinct from surrounding tissue. Semisolid (e.g. milia) or fluid-filled.