Bedside Tests in Dermatology

Magnification

The most important tool for a dermatologist is a hand lens. It is a convex lens with a magnification of 5X-7X.

Diascopy

A glass slide is taken and pressed on the skin. It is used:

1. To differentiate between erythema and purpura: When there is simple erythema due to vasodilation, If you press, the blood spills out to the sides. So, there will be a blanching effect. In purpura, there will be no change because it is either due to vasculitis or extravasation of RBCs.
2. To differentiate between nevus anemicus and depigmentosis
   • In depigmentosis- no change.
   • In nevus anemicus- merges with the surrounding skin.
3. To see Apple jelly nodules- seen in 
   • Lupus vulgaris 
   • Sarcoidosis 

Wood’s Lamp 

Wood’s lamp is a low-output mercury arc amp. It is Covered by a wood filter, which is made of Barium silicate and 9% nickel oxide. It emits light with a wavelength of 320-450nm. The peak wavelength can be 365nm. Wood’s lamp examination is done in a dark room.

The lamp is Put on and let it get warmed for a minute on the suspected lesion. Observe the fluorescence produced.

It is used in tinea capitis, pityriasis versicolor, and erythrasma (it produces Coral red fluorescence in erythrasma).

It helps to differentiate nevus de pigmentosus. In the presence of a wood lamp, nevus will accentuate.

It can be used in vitiligo. Vitilogy can accentuate on wood’s lamp examination.

It can be used in congenital erythropoietic porphyrias.. Fluorescence can be observed in teeth and urine.

It is used in melasma. Epidermal pigmentation will accentuate. So, there will be no much change in dermal pigmentation.

Smears

Smears are also used at the bedside of the patient for the diagnosis of dermatological pathologies. Smears can be 

• Potassium Hydroxide KOH
• TZANCK
• GRAM’s
• Wet preparation 
• Tissue smear
• Mite demonstration 
• Slit skin smear 

KOH Smear

KOH smear is used in fungal infections. Candida KOH mount will show Budding yeast cells. In Dermatophytes, multiple branching hyphae are seen.

Pityriasis versicolor on KOH shows a spaghetti and cheese ball appearance. 

Tinea capitis KOH smear is used to distinguish ectothrix and endothrix in Tinea capitis. In ectothrix, spores are outside the hair shaft. In endothrix, spores are inside the hair shaft.

TZANCK Smear

Wet Smear

A wet smear test is done for trichomoniasis and Bacterial vaginosis. In Trichomoniasis, a pear-shaped structure is seen making jerky movements. In Bacterial vaginosis, closed cells are seen.

Tissue Smear

A tissue smear test is done in Molluscum, where LD bodies are seen. It is also seen in Donovanosis, where a Safety pin appearance is seen.

Mite Demonstration

Mite demonstration is done in scabies where on examination, Eggs, mites, and skybella are seen.

Slit Skin Smear

The ear lobe is pinched, and take a no.15 scalpel blade with 5mm length and 3mm width. Then, take a smear. A slit skin smear test is done for Leprosy and in Leishmaniasis to demonstrate LD bodies.

Gram Stain

Gram stain is the most common microbiological investigation. It is used to diagnose various bacterial infections. In impetigo, gram-positive cocci in clusters are seen. In chancroid, the appearance of the rail track or fish and stream is seen.

In gonococcal urethritis, intracellular diplococci are seen.

Dark Ground Microscopy

Dark ground microscopy is done for Treponema pallidum. Treponema pallidum is responsible for syphilis, which is an STI.

Patch Test

The patch test is done for  Eczema.

Skin Biopsy

Although it is not a bedside test, the sample can be taken bedside and then tested later. If there is a lesion or plaque, an incisional biopsy is done. A small biopsy is taken from the plaque.

An excisional biopsy is done on a Lesion suspected of being a tumor or premalignant condition. The whole lesion must be removed. This is called an excisional Biopsy.

If the lesion is present superficially on the skin, a shave biopsy is done. A scalpel or blade is used to shave the lesion off from the surface. This can be done for Actinic Keratosis and Naevi. 

Incisional Biopsy 

There are two ways to perform incision biopsy:

1. Incisional biopsy: A small elliptical incision is taken. The Disadvantage is that it produces Ragged margins.  
2. Punch biopsy: A punch is used and inserted into the skin to take a perfectly round biopsy. It heals very well. It is the most common type of biopsy. The advantages of punch biopsy are:
   • Very convenient 
   • Punches come in various sizes like 3mm, 4mm, 5mm etc.
   • Healing is very good.
   • Has a perfect circular margin.

Frequently asked questions

Q: What is the most common type of excision biopsy?

Answer: Punch Biopsy

Q: What cells are seen in the tzank smear of pemphigus?

Answer: Acantholytic Cells

Q: What disease shows spaghetti and meatballs appearance on KOH mount?

Answer: Pityriasis Versicolor

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