Education: Pictorial case study

Contributed by Dr Jean Watkins, a retired GP in Hampshire

The case
This 25-year-old woman had been in India for a holiday and developed an ulcerated, crusted plaque on her knee. The condition was assumed to be impetigo and she was prescribed topical fusidic acid cream and oral flucloxacillin.

There was no improvement after a year, so a biopsy of the lesion was taken by a dermatologist.

Histology showed inflammatory infiltrate of the upper dermis, lymphocytes, plasma cells and giant cells and microbiology revealed Mycobacterium tuberculosis. Her chest X-ray was normal.

Diagnosis and management
Lupus vulgaris commonly occurs on the head and neck. A persistent, reddish/brown plaque develops, which may display red-brown nodules.

In some cases the lesion may be scaly or ulcerate. Lesions may persist for years and on clearing there will be residual scarring.

The diagnosis is confirmed by biopsy and culture of M tuberculosis with a check on sensitivities. A chest X-ray and three sputum specimens should be taken to rule out pulmonary involvement.

Treatment is with antitubercular drugs and six months of isoniazid and rifampicin, with pyrazinamide and ethambutol for the first two months. Surgery may be required for hypertrophic or verrucous lesions.

Possible different diagnoses

  • Bowen's disease.
  • Squamous cell carcinoma.
  • Psoriasis.
  • Pyoderma gangrenosum.
  • Sarcoidosis.
  • Leprosy.
  • Pityriasis lichenoides.

Differential diagnosis

Pyoderma gangrenosum (PG)

  • Uncommon cause of skin ulceration that occurs on the legs in the over fifties.
  • About half of patients with PG have an underlying problem, such as ulcerative colitis, Crohn's disease, rheumatoid arthritis, chronic active hepatitis, or myeloid blood dyscrasias.
  • Usually sudden onset of small red pustule that breaks down leading to ulceration.
  • Clinical diagnosis but biopsy may be required.
  • Swab for culture and sensitivities to check for secondary infection.

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