Practical notes on clincal dermatology
Dermatology is a morphologically oriented specialty. As in all specialties the medical history is important, however, the ability to interpret the findings is even more important. The diagnosis of skin disease must be approached in an orderly and logical manner, and the temptation to make rapid judgments after hasty aberration must be controlled. The recommended approach to the patient with skin disease is as follows:
Obtain a brief history from the patient especially, noting; duration rate of onset, location, symptoms, previous episodes, family history, history of exposure to allergens, occupation, and previous treatment.
Determine the extent of the eruption by uncovering the patient completely.
Determine the primary lesions with the help of a hand lance.
Determine the nature of any secondary or special lesions.
Formulate a differential diagnosis.
- Obtain a skin biopsy and the following laboratory tests;
- 10-20% potassium hydroxide (helps in the diagnosis of fungal infection of the skin) .
- Skin scrapings for scabies.
- Gram stain
-Fungal and bacterial cultures
-Cytology (T zanck smear)
-Woods light examination
-Patch tests
-Dark field examination and blood tests studies.
How is a KOH examination performed?
The highest rate of recovery of organisms occurs in specimens taken from the tops of vesicles and the edges of annular lesions. The site should be swabbed with an alcohol pad or water and scraped with a #15 blade. The moist corneocytes are then easily transferred from the blade to a glass slide. One or two drops of KOH (10-20%) are added, and the specimen is cover-slipped. The KOH preparation is gently warmed, but not boiled, and then examined under the microscope. It is important to focus back and forth the material ,so that the refractile hyphae can be found. Fungal hyphae can be recognized by their regular cylindrical shapes with branching and presence of septa. Older lesions may demonstrate numerous rounded spores called arthrospores.