Macules
A macule is a flat, demarcated, abnormally coloured area of skin of any size. It may be red (e.g. drug eruption), dark red (e.g. purpura), brown (e.g. a flat mole) or white (e.g. pityriasis versicolor). Purpura is described elsewhere (see ‘Purpura and petechiae’). There is some crossover between erythema (see ‘Erythema’) and red macules.
Differential diagnosis
Common Diagnoses
- Drug Reaction/Allergy
- Flat Mole (Junctional Naevus)
- Non-Specific Viral Exanthem
- Sun-induced Freckles (Including Solar Lentigines)
- Chloasma
Occasional Diagnoses
- Measles and Rubella
- Post-inflammatory Hypo- or Hyperpigmentation
- Café Au Lait Spot (Creamy Brown) and Mongolian Spot (Brown or Slate-Grey)
- Berloque Dermatitis (Brown: Chemical Photosensitisation, e.g. Bergamot Oil)
- Depigmentation: Vitiligo, Pityriasis Versicolor, Pityriasis Alba
Rare Diagnoses
- Infections: Macular Syphilide, Tuberculoid Leprosy, Typhoid (Rose Spots in 40%)
- Albright’s Syndrome
- Neurofibromatosis (Associated with more than Six Café Au Lait Spots)
- Pathological Freckles: Hutchinson’s Freckle, Peutz–Jeghers Syndrome
- Naevus Anaemicus (Permanent Vasoconstriction Due to Neurovascular Abnormality)
Ready reckoner
Key distinguishing features of the most common diagnoses
| Drug Reaction | Flat Mole | Viral | Freckles | Chloasma | |
|---|---|---|---|---|---|
| Itching and Burning | Yes | No | No | No | No |
| Variable Pigmentation | No | Yes | No | Possible | Possible |
| Red | Yes | No | Yes | No | No |
| <0.5 cm Diameter | Possible | Possible | Possible | Yes | No |
| Symmetrical, Muzzle Area | No | No | No | No | Yes |
Possible investigations
- There are very few relevant investigations to consider and they would be required only exceptionally, as the diagnosis is usually clinical. Skin scrapings for mycology or fluorescence under Wood’s light may help in the diagnosis of pityriasis versicolor; acute and convalescent serum samples may confirm rubella; serology for syphilis may be appropriate with an unusual macular rash; and very occasionally, a skin biopsy may be required to clinch an obscure diagnosis.
Top Tips
- A drug eruption can take two weeks to appear from the time of the first dose – so don’t be misled by the fact that a course of antibiotics may have been completed some days before the related drug rash develops
- Pityriasis versicolor may be misdiagnosed as vitiligo. If in doubt, take scrapings for mycology or examine under Wood’s light.
- Odd lines of hyperpigmentation on the sides of the neck are likely to be Berloque dermatitis – a photosensitive rash caused by oil of bergamot, present in perfumes.
Red Flags
- Hutchinson’s freckle is a giant, variegated freckle, seen in elderly sun-exposed skin. There is a high risk of malignant change, so refer.
- Rubella is rare, but may become commoner as a result of media coverage of ‘immunisation scares’. Establish whether or not a young woman presenting with a rubella-type rash is pregnant – if she is, confirm her rubella status.
- A child with very many freckles on and around the lips may have Peutz–Jeghers syndrome. This is associated with small bowel polyposis.
- Vitiligo tends to have a poor prognosis in Caucasians, especially if it is widespread and affecting lips and extremities.