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
- 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)
- Measles
- Pityriasis Alba
- Pityriasis Versicolor
- Rubella
- Vitiligo
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.