Tuesday, 6 March 2012

Situations to remember (2)




Wood’s light does the trick

On asking a pharmacist to recommend a dermatologist, the young man came to see me. He has seen five professors in vain, one of whom biopsied his skin disease with non-specific histopathological findings. While listening to the history, I immediately saw the difficulty in reaching the correct diagnosis. Various diagnoses have been made by the colleagues, e.g. insect bites and scabies. One of the professors has prescribed systemic steroid for the “unknown skin disease”. Four of the professors had gathered to discuss his case at university in vain before the fifth professor biopsied his skin disease. From time to time, Wood’s light does the trick. There were scratch marks and conspicuous lichenification involving many areas including the groins and the perianal skin. Presence of extensive coral-red fluorescence under Wood’s light clinched the diagnosis. Erythrasma can certainly be symptomless but scratching leading to lichenification might occur. This was the first time for him to be examined under Wood’s light and the erythrasma patches were apparently difficult to see by the colleagues because of his hairy skin. Coral-red fluorescence with Wood’s light is attributable to coproporphyrin III and strongly suggests erythrasma.



Erythrasma has been described by pathologists as an "invisible dermatosis". In other words, section stained with haematoxylin and eosin appears normal. Small coccobacilli can be seen in the superficial part of the stratum corneum in Gram preparations. They are also seen in PAS (periodic acid–Schiff) and methenamine silver preparations. Actually, scrapings from the affected skin may show the bacteria if stained with Gram or even with simple potassium hydroxide clearance. Culture colonies fluoresce coral red under Wood’s light after 18–36 hours. Such confirmation is not normally necessary when it is diagnosed clinically and Wood’s light examination of the patient is positive.


This page was last updated in March 2012.

Main Works of Reference List (The first eight are my top favourites)

  • British National Formulary
  • British National Formulary for Children
  • Guidelines (BAD - BASHH - BHIVA - Uroweb)
  • Oxford Handbook of Genitourinary Medicine, HIV, and Sexual Health
  • Oxford Handbook of Medical Dermatology
  • Rook's Textbook of Dermatology
  • Simple Skin Surgery
  • Weedon's Skin Pathology
  • A Concise Atlas of Dermatopathology (P Mckee)
  • Ackerman's Resolving Quandaries in Dermatology, Pathology and Dermatopathology
  • Andrews' Diseases of the Skin
  • Andrology (Nieschlag E FRCP, Behre M and Nieschlag S)
  • Bailey and Love's Short Practice of Surgery
  • Davidson's Essentials of Medicine
  • Davidson's Principles and Practice of Medicine
  • Fitzpatrick's Colour Atlas and Synopsis of Clinical Dermatology (Klaus Wolff FRCP and Richard Allen Johnson)
  • Fitzpatrick’s Dermatology in General Medicine
  • Ganong's Review of Medical Physiology
  • Gray's Anatomy
  • Hamilton Bailey's Demonstrations of Physical Signs in Clinical Surgery
  • Hutchison's Clinical Methods
  • Lever's Histopathology of the Skin
  • Lever's Histopathology of the Skin (Atlas and Synopsis)
  • Macleod's Clinical Examination
  • Martindale: The Complete Drug Reference
  • Oxford Handbook of Clinical Examination and Practical Skills
  • Oxford Textbook of Medicine
  • Practical Dermatopathology (R Rapini)
  • Sexually Transmitted Diseases (Holmes K et al)
  • Statistics in Clinical Practice (D Coggon FRCP)
  • Stockley's Drug Interactions
  • Treatment of Skin Disease: Comprehensive Therapeutic Strategies
  • Yen & Jaffe's Reproductive Endocrinology