Differential Diagnosis

Common Diagnoses

  • Sebaceous Cyst
  • Lipoma
  • Basal Cell Carcinoma (BCC)
  • Warts
  • Xanthoma

Occasional Diagnoses

Rare Diagnoses

  • Malignant Melanoma (becoming more common in the UK)
  • Vasculitic: Erythema Nodosum, Nodular Vasculitis, Polyarteritis Nodosa
  • Atypical Infections (e.g. Leprosy, Treponema, Lupus Vulgaris, Fish Tank and Swimming Pool Granuloma, Actinomycosis)
  • Lymphoma and Metastatic Secondary Carcinoma
  • Sarcoidosis
  • Pretibial Myxoedema

Ready Reckoner

Key distinguishing features of the most common diagnoses

XanthomaSebaceous CystBCCWartLipoma
Central PunctumNoYesNoNoNo
Characteristic DistributionYesNoYesNoNo
Normal Skin SurfaceNoYesNoNoYes

Possible Investigations

Likely:None (skin biopsy or cytology if doubt about the lesion or clinical diagnosis of possible carcinoma).

Possible:Lipid profile, FBC, ESR/CRP, urate, rheumatoid factor/anti-CCP, urinalysis.

Small Print:TFT, skin biopsy, further investigations guided by clinical picture (see below).

  • Excision biopsy is the definitive investigation for achieving a diagnosis; cytology from skin scrapings can be used to diagnose BCC.
  • Lipid profile: Xanthomata require a full lipid profile to define any underlying hyperlipidaemia.
  • Urinalysis: If suspect inflammatory or vasculitic skin lumps, as may reveal proteinuria if associated with systemic and renal disorders.
  • FBC and ESR/CRP: ESR/CRP raised in inflammatory disorders and malignancy; may also reveal anaemia of chronic disease or malignancy (including lymphoma).
  • Check urate if gouty tophi are clinically likely.
  • Rheumatoid factor/anti-CCP: Nodules are usually associated with positive rheumatoid factor.
  • TFT: To diagnose Graves’s disease with pretibial myxoedema.
  • Skin biopsy: May contribute to a diagnosis of sarcoidosis
  • Further investigations according to clinical picture: Some lesions, such as erythema nodosum, may require further investigation to establish the underlying cause; histological confirmation of skin secondaries may similarly require further assessment, although the overall condition of the patient may mean this is a futile exercise.

Top Tips

  • Look at the lesion under the magnifying glass – this may reveal suspicious signs such as ulceration or a rolled, pearly edge.
  • In uncertain cases which do not require urgent attention, record your findings carefully (including precise dimensions) and review in a month or two.
  • Stoical patients may underestimate the significance of a suspicious lesion, particularly if you discover it during a routine examination – if you are referring them for biopsy, impress upon them the need to attend their appointment.
  • Establish the patient’s concern, which will usually centre on worries about cosmetic appearance or cancer. This will result in a more functional consultation and a more satisfied patient.

Red Flags

  • Night sweats and itching with skin nodules raises the suspicion of lymphoma. Examine lymph nodes, liver and spleen carefully.
  • The elderly patient complaining of a lesion in a sun-exposed area which ‘just won’t heal’ may well have a squamous or basal cell carcinoma.
  • The appearance of a nodule in a mole is highly significant and requires referral.
  • A patient with nodulocystic acne requires referral to a dermatologist for possible treatment with 13-cis-retinoic acid.
  • The unwell middle-aged or elderly patient who develops bizarre and widespread skin nodules over a period of a few weeks probably has an underlying carcinoma.
Report errors, or incorrect content by clicking here.