Dermatology Diagnostic techniques

Question 1

1-What is a Wood Lamp?

2-What makes up the Wood filter?

Answer 1

1-A device that emits long-wave UV light (black light) that is filtered by a Wood filter, allowing only a band of UV light between 320 and 400nm (peak, 365nm) to be emitted.

2-Barium Silicate & Nickel Oxide

Question 2

1-What are seven conditions Wood Lamp can be of diagnostic assistance?

Answer 2

1-a) Fluorescent species of Tinea Capitis b) Erythrasma c) Porphyrias e.g. Porphyria Cutanea Tarda d) Propionibacterium Acnes in Acne Vulgaris e) Demonstration of hypopigmentation vs depigmentation in light skinned individuals f)Pseudomonas Aeroginosa infection g) Detection of Tetracycline infection in children’s teeth

Question 3

1-What compound in fluorescent species of Tinea Capitis gives off the yellow/green or blue/green light?

2-What is the limitation of Woods Light in Tinea Capitis?

3-What is one of the most common fluorescent species in Tinea Capitis?

Answer 3

1-Pteridine (do not confuse this with lint from clothing that may fluoresce a white colour)

2-Most Tinea Capitis infections are due to nonfluorescent species, e.g. Trichophyton tonsurans

3-Michrosporum Canis (5-10% of cases)

Question 4

1a) What is the coral red fluorescence in erythrasma due to? b) What bacteria is it produced by?
c) What is a limitation of Woods Light in this diagnosis?

Answer 4

1a-Porphyrin (coproporphyrin III)

b) Corynebacterium
c) Porphyrins are water soluble, so if the patient has recently bathed the test will be negative as the porphyrins will be washed off.

Question 5

1-What colour fluorescence is Pseudomonas Aeruginosa under Wood Light?

2-What pigment is the fluorescence due to?

Answer 5

1-Greenish fluorescence

2-Pyoverdin

Question 6

1-What can be used to diagnose dermatophytes and yeast infections of the skin and mucous membranes?

2-What technique can be used to diagnose scabies?

3a-What preparation is a microscopic examination of cells obtained from the base of vesicles?

b) What diagnosis can this preparation assist to make?

Answer 6

1-Potassium Hydroxide preparation (KOH)

2-Mineral Oil preparation

3a-Tzanck Preparation

b-HSV, VZV, incl chicken pox and herpes

Question 7

1-What are the two different techniques used in a shave biopsy?

2-What is the specific name for a biopsy completed with a razor blade?

3-In what instance is this superior to punch biopsy?

Answer 7

1-Razor blade and scalpel blade techniques

2-Saucerization

3-In bullous disorders, as the twisting motion of a punch biopsy is likely to separate the top and base of the blister, hindering interpretation

Question 8

1-When is a punch biopsy indicated?

Answer 8

1-When sampling is required for the assessment of most inflammatory skin conditions