ISSN 2398-2942      

Skin: Wood's lamp test

icanis
Contributor(s):

Catherine Fraser


Introduction

  • The tryptophan metabolites of certain dermatophytes, eg Microsporum canis Microsporum canis fluoresce under ultra-violet light of 330-365 nm wavelength Ringworm Woods lamp.
  • A Wood's lamp is a source of ultra-violet light filtered through a cobalt or nickel filter.
  • Microsporum canis is the only dermatophyte species of importance in veterinary medicine which fluoresces.

Uses

  • Screening for Microsporum canis Microsporum canis infection.
  • Selection of appropriate hairs for culture.
  • Not effective to monitor infection.
    Positive Wood's lamp examination is only suggestive, not diagnostic, of Microsporum canis infection.
    Negative Wood's lamp examination does not rule out Microsporum canis infection as up to 50% of strains of M. canis do not fluoresce.

Advantages

  • Rapid screening technique.

Disadvantages

  • Not all strains of Microsporum canis fluoresce - 30-50% show positive fluorescence.
  • Medication, eg iodine, destroys fluorescence.
  • Only actively infected growing hairs fluoresce.

Requirements

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Preparation

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Procedure

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Outcomes

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Prognosis

  • Non-fluorescing strain of Microsporum.
  • Lamp not warmed up before performing test.
  • Hairs not exposed to UV for sufficient length of time (>5 min in some cases).
  • False positive: over-interpretation of results due to scale, drug therapy or certain bacteria.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Sparkes A H, Stokes C R, Gruffydd-Jones T J (1995) Experimental Microsporum canis infection in cats - correlation between immunological and clinical observations. J Med Vet Mycol 33 (3), 177-184 PubMed.
  • Sparkes A H, Gruffydd-Jones T J, Shaw S E et al (1993) Epidemiological and diagnostic features of canine and feline dermatophytosis in the United Kingdom from 1956 to 1991. Vet Rec 133 (3), 57-61 PubMed.
  • Caplan R M (1967) Medical uses of Wood's lamp. JAMA 202 (11), 1035-1038 PubMed.

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