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Diagnosis of ringworm

By Dr Ananya Mandal, MD

Ringworm is a fungal skin infection that is most commonly diagnosed clinically by its appearance.

The name is derived from the characteristic skin lesion that appears like a ring. The center of the ring remains pale, shiny and flaky while the edges are red, inflamed and blister filled that may ooze or crust.

The lesions are in addition itchy.

Ringworm is caused by dermatophytes that live on the tough tissue keratin that likes skin, hair and nails. Ringworm infection thus commonly affects these structures.

Clinical diagnosis of ringworm

Clinical diagnosis depends on symptoms and location of the lesions.

For example:

  • scalp ringworm or tinea capitis lies over the scalp,
  • body ringworm or tinea corporis may affect any part of the body,
  • athlete’s foot (tinea pedis) affects the foot,
  • jock’s itch (tinea corporis) affects the groin,
  • nail ring worm affects the nail beds,
  • facial ring worm (tinea barbae) lies over the beard area etc.

Treatment of ringworm

In most cases treatment is begun on the basis of clinical diagnosis. However, in some individuals tests may be needed to diagnose and confirm ringworm infections.

These are needed if the symptoms are severe or if they fail to respond to initial over-the-counter antifungal treatment.

Diagnosis that needs to be rule out when confirming ring worm infections include Candidial infections (another type of fungal infection), skin lesions due to allergies or abrasions, diseases like psoriasis and seborrhea (dandruff) etc. (1-4)

Specific diagnostic methods

Specific diagnostic methods of ringworm detection include inspection of clinical material, wood’s lamp examination and so forth. (2-4)

Inspection of the clinical material

The physician may collect tiny bits of infected tissues for examination. This could be skin scraping, nail clipping or bits of hair.

This material is removed using a scalpel, tweezers, or a curette that firmly scrapes the lesion, particularly at the advancing border.

The blisters are often rich in the fungal spores and may be collected as sample.

Skin and nail specimens may be scraped directly onto special black cards for easy viewing and transportation to the laboratory.

The sample is then examined under the microscope using chemicals like 10 to 20% Potassium hydroxide or stains like Parker ink or calcofluor white mounts. This helps better visualization.

It takes less than 24 hours for examination. On examination the microscope reveals the tiny thread like fungi with typical branching patterns and rod-shaped filaments of uniform width with lines of separation.

Diagnosis is confirmed after culture of the fungi.

Wood's lamp examination (ultraviolet light)

This light shows up the fungi present in the sample. This is of limited usefulness.

Culture

The specimens with the fungi are placed on favourable medium called Sabouraud's dextrose agar containing cycloheximide (actidione).

They are left in isolation at 26-28C for 4 weeks. In case of a positive infection there is growth of the affecting dermatophyte.

Blood tests

Blood tests for fungal identification are not useful.

Biopsy

If diagnosis is difficult, skin or nail biopsy may be needed.

Edited by , BA Hons (Cantab)

Further Reading

What is ringworm?
Ringworm Causes
Ringworm Symptoms
Ringworm Treatments

Last Updated: Jul 2, 2012

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