Dermatologic Diagnostic Tests and Procedures
Anne Marie Ruszkowski Lord
Noreen Heer Nicol
OBJECTIVES
After studying this chapter, the reader will be able to:
Identify diagnostic tests and procedures commonly used on the skin, including microscopic examination, cultures, biopsy for removal and/or pathology, and patch testing.
Describe important steps of above tests and procedures, including scrapings and swabs for microbiology, virology, and mycology.
Describe techniques and application for patch testing in the evaluation of contact dermatitis.
Provide effective education to patients and families to prepare them for tests and procedures.
KEY POINTS
The skin is a highly accessible organ, making it available for several diagnostic tests that can help identify specific skin diseases.
Diagnostic tests performed directly on the skin that are usually minimally traumatic and often highly rewarding diagnostically include microscopic examinations, cultures, biopsies, and patch testing.
Blood, urine, and radiograph testing remain helpful when systemic disease is suspected.
Sample selection is extremely important in obtaining the proper diagnostic specimen.
Nursing staff is encouraged to understand each procedure and the benefit versus risk of each to teach and care for their patients more effectively.
Patch testing is an essential tool used in diagnosing allergic contact dermatitis.
Nursing and allied health staff are frequently key personnel participating in the preparation, interpretation, and placement of patch tests.
I. DIAGNOSTIC AIDS
As adjuncts to what is seen with the eyes or palpated with the hands, numerous diagnostic tools offer key information in making a diagnosis. Nursing staff rarely perform all steps independently in diagnostic procedures used to establish skin disorders. Therefore, this section is meant to provide an overview. Correct visualization and sample selection are critically important in obtaining the proper diagnostic specimen.
A. An alcohol wipe swept across a lesion is a method used to elucidate the small, delicate telangiectasia and translucence of that lesion, such as with a basal cell carcinoma.
B. Diascopy examination of the skin is completed by gentle pressure utilizing a translucent object, such as a glass slide, to observe the effect upon the color (erythema) of the skin.
1. Pressure producing a reduction in erythema or pigmentation indicates blood vessel dilation.
2. Pressure that does not produce a change in erythema or pigment indicates increased extravasation of blood, or simply an increased amount of pigment.
C. Mineral oil applied to a glass slide before using magnification helps visualize certain specimens, such as the scabies mite.
D. The microbe is stained for visibility in many microscopic examinations. In dark-field examination, the slide background is darkened to visualize the causative spirochete for syphilis. Specimens for dark-field examinations must be examined immediately.
II. DIAGNOSTIC TESTS
KOH (potassium hydroxide) preparation is a diagnostic method used to confirm the presence or absence of hyphae, spores, and pseudospores. A 10% to 20% KOH solution will digest the keratin in tissue but leave most fungal forms intact for visualization under the microscope (Figure 3-1).
A. Certain fungi have characteristic appearances.
1. A no. 15 blade is used to scrape skin/scale from the edge of a scaling lesion onto a glass slide. The extremely thick pieces of scale should be avoided. If Candida infection is suspected, a pustule can be a good source of material for the exam.
2. With the edge of the no. 15 blade, sweep scale or matter into a small pile in the center of the slide.
3. One or two drops of 10% KOH are placed on the slide.
4. A glass coverslip is applied over specimens. Blot out the excess KOH by firmly pressing a paper towel on top of the coverslip and slide.
5. The slide is gently heated to dissolve the keratin, and the coverslip is gently squeezed and then examined under
the microscope using low illumination. If a heat source is not available, leave the specimen set for a minimum of 30 minutes after applying the KOH prior to examination. Scan the entire coverslip first under low (X10) power and then move to higher (X45) power for confirmation.
the microscope using low illumination. If a heat source is not available, leave the specimen set for a minimum of 30 minutes after applying the KOH prior to examination. Scan the entire coverslip first under low (X10) power and then move to higher (X45) power for confirmation.
 FIGURE 3-1. KOH solution and slide. (From Goodheart, H. P. (2003). Goodheart’s photoguide of common skin disorders (2nd ed.). Philadelphia, PA: Lippincott Williams & Wilkins.) |
6. Repeat the process with a new specimen if the test is negative and a high degree of suspicion remains for a fungal disorder.
B. Fungal cultures are a frequent next step when exact fungal species need to be determined to assist in treatment or the KOH test is negative in light of high suspicion of fungal disease. Scrapings obtained as above with a no. 15 blade from a dry patch of skin, intact pustule, or nail plate or from under the nail can be introduced onto a dermatophyte culture medium and aerobically incubated for a minimum of 7 to 10 days or per the specific media directions. The time required for results depends greatly on the media, lab, or process.
C. Wood’s Fluoresence lamp is another simple, but less used, diagnostic tool. This handheld lamp has ultraviolet bulbs (365 nm) that cause certain microorganisms to appear colorful when illuminated. The use of this test has become limited because some common organisms do not fluoresce. This includes T. tonsurans which is now the most common cause of tinea capitis in the U.S. (Figure 3-2).
1. Certain fungus or ringworms glow blue-gray or yellow-green.
2. Tinea versicolor can appear gold.
3. Urine screen for porphyrins fluoresces orange.
D. Tzanck smear uses a microscope and special stain including Giemsa, methylene blue, or Wright stain. The specimen is best taken from the base of a new vesicle. The specimen slide is colored with a special dye and examined under a microscope, either at the practice office or at a pathology laboratory. The examiner looks for abnormally large cells (called giant cells) that are characteristic of herpes virus infections. This tool aids in the diagnosis of herpes simplex (which causes fever blisters) or herpes zoster (which causes chickenpox and shingles), but does not distinguish between the two.
 FIGURE 3-2. Vitiligo as seen with Wood’s lamp. (From Goodheart, H. P. 2010. Goodheart’s same-site differential diagnosis: A rapid method of diagnosing and treating common skin disorders. Philadelphia, PA: Wolters Kluwer.) |
E. Viral culture, like Tzanck smear, is ideally taken from intact vesicles and transported in a viral transport media. A vesicle is opened or crust removed and underlying serum is swabbed. The swab is placed in the viral media. Human virus types that can be identified by viral culture include adenoviruses, Cytomegalovirus, enteroviruses, herpes simplex virus, influenza viruses, parainfluenza viruses, varicella-zoster virus, measles, and mumps. Viral PCR (polymerase chain reaction) test is also frequently used.
F. Bacterial culture or microbiological culture is a method of multiplying microbial organisms by letting them reproduce in predetermined culture media under controlled laboratory conditions. The ideal specimen sources for bacterial cultures include intact pustules, bullae, and abscesses. The specimen can be obtained by a variety of methods ranging from swabbing, scrapping, aspiration, or biopsy. The cultures are used to determine the type of organism, its abundance in the sample being tested, or both.
G. Scabies scrapings are done with an oil-moistened no. 15 blade. Vigorously scrape small papules or questionable burrows, transfer to a glass slide, cover with coverslip, and examine microscopically.
H. Direct immunofluorescence of tissue is an option when trying to diagnose immunologic abnormalities in the skin. Bullous diseases and connective tissue disorders are two examples. Special tissue preparations and stains are done at a lab to microscopically visualize immunoglobulins, complement, and fibrin found in the skin or circulation.
I. Gram stain allows for identification of Gram-negative or Gram-positive organisms. Exudate from the site is smeared onto a glass slide, then stained, dried, and examined under oil immersion.
J. Hair pull (pluck) is the most accurate technique to evaluate the anagen/telogen ratio. Approximately 50 hairs of the same length are extracted using a rubber-tipped needle holder and plucked with a quick motion. Hairs are floated on a wet microscope slide or Petri dish for examination.
Dyes will be applied to determine phase of growth—anagen reacts with citrulline; telogen hairs do not stain. Hair can also be examined under a microscope to evaluate for disorders such as Netherton disease.
Dyes will be applied to determine phase of growth—anagen reacts with citrulline; telogen hairs do not stain. Hair can also be examined under a microscope to evaluate for disorders such as Netherton disease.
III. SKIN BIOPSIES
Shave, punch, and ellipse are biopsy techniques used in both diagnosis and treatment of skin diseases.
A. Shave biopsy/excision is a tangential specimen of tissue for pathology, resulting in minimal to no scarring.
1. The shave biopsy/excision is indicated for dome-shaped intradermal nevi, fibromas, warts, seborrheic keratoses, and actinic keratoses.
2. A portion of the epidermis and underlying papillary dermis is primarily involved.
3. The procedure can be both an excisional and incisional biopsy depending on whether part or all of the lesion is removed. Extremely superficial lesions are frequently removed with this method.
4. The equipment needed includes local anesthesia, gentian marker, a single-edged blade (Figure 3-3), curette (optional), hemostatic agent, pathology bottle, and appropriate dressing.
5. Postbiopsy wound care or dressings are optional depending upon the shave location and patient compliance.
6. Hypopigmentation at the shave site and localized infection are two potential complications.
 FIGURE 3-3. Straight blade and punch tools. A: Shave biopsy. A scalpel blade is manipulated by the operator to adjust the depth of the biopsy. Hemostasis is achieved with topical application of aqueous aluminum chloride, ferrous subsulfate, or electrocautery. B: Punch biopsy. The operator makes a circular incision to the level of the superficial fat, using a rotating or twisting motion of the trephine. Traction applied perpendicularly to the relaxed skin tension lines minimizes redundancy at closure. Hemostasis is commonly achieved by placement of sutures. (From DeVita, V. T., et al. 2014. DeVita, Hellman, and Rosenberg’s cancer: Principles & practice of oncology. Philadelphia, PA: Wolters Kluwer.) |
B. Punch biopsy has multiple uses: diagnosing a disease or an eruption, or simply excising a lesion. The punch instrument can be either circular or elliptical with a razor-sharp cutting edge (see Figure 3-3).
1. An early lesion is selected when an eruption needs diagnosing. If a vesicle is to be studied, a fully intact one is preferred.
2. An older lesion is needed if discoid lupus erythematosus is suspected.
3. A punch tool is advantageous in the removal of small nevi because the scar will be smaller than one from the elliptical method.
4. A punch biopsy is commonly used in diagnosing basal and squamous cell carcinomas, granuloma annulare, and other diseases that involve the deeper dermis.
5. Punch diameters are available in multiple sizes. Those most frequently used in dermatology range from 2.0 to 8.0 mm.
6. For local anesthesia, lidocaine 1%, usually with epinephrine for less bleeding depending on the site location, is administered with a 30-gauge needle by raising a wheal prior to biopsy.
7. Depth extends from the stratum corneum (outermost skin layer) to the underlying fat, providing the entire dermis for evaluation. If nonabsorbable suture is used, the patient returns for suture removal. The punch is twisted while obtaining the biopsy to sample the epidermal and deeper dermal tissue.
8. Complications to consider are infection, scarring, and nerve damage.
C. Elliptical excision/wedge biopsy is used when both normal skin and lesional skin junctions are needed for study, such as evaluating basal and squamous cell malignancies and nevi.
1. The biopsy offers greater tissue depth down to and, if necessary, into the subcutaneous fat.
2. The equipment needed includes local anesthesia, gentian marker, sterile gloves, a single-edged blade with handle, needle holder, small forceps, skin hook, small clamp, small pointed scissors, suture, curette (optional), hemostatic agent, pathology bottle, gauze, and appropriate dressing.
3. The incision length is normally 2.5 to 3 times the width of the incision.
4. Repairs require suturing, and layered closures are frequently necessary.
5. With so many different types of absorbable suture material available, patients may not need to return for suture removal, making skin surgery more convenient for their schedules. Nonabsorbable suture must be removed. The number of days until removal of nonabsorbable suture is dependent on the area of incision. For instance, facial sutures are removed earlier at 5 to 6 days versus trunk or extremity sutures, which might be left in place 1 to 2 weeks.
6. Flaps and grafts are additional options for closing large and/or inelastic skin surgery sites.
7. Scarring, possible nerve damage, and infection are the most common complications.
8. Mohs technique is a specialized procedure involving serial excisions of tissue that are systematically mapped and microscopically examined. This technique done by specially trained Mohs surgeons is used to treat basal cell and squamous cell carcinomas. It defines the extent of the cancer and ensures that the surgical margins are free of tumor.
IV. CRYOSURGERY
A. Definition. The destruction of tissue through freezing, most commonly with liquid nitrogen; it causes less scarring because of the ability to control the depth of tissue destruction. It is the simplest and least invasive method of lesion destruction, but one that yields no tissue for pathology.
B. Cryosurgery is the process of destruction by applying extreme cold to a localized site, causing ice formation at the cellular level, thermal shock to the cell, and vascular stasis, resulting in necrosis. Liquid nitrogen at -195.6°C is the standard agent used because of its availability and low cost, and because it is noncombustible (Figure 3-4).
1. The liquid nitrogen invokes rapid cooling and slow thawing and may be applied using a direct spray or cotton-tipped applicator.
2. Treatment causes intense stinging and burning that generally peaks 2 minutes later.
C. Indications
1. Actinic keratoses
2. Thin seborrheic keratosis
3. Leukoplakia
4. Molluscum contagiosum
5. Common and genital warts
6. Superficial basal cell carcinoma (BCC) and squamous cell carcinoma (SCC) in situ (rarely)
D. Nursing considerations
1. Good cosmetic results with little anesthesia.
2. Painful when used to treat lesions on nose, lips, ears, or eyelids; severe pain if palms, soles, or confined areas such as the area around the nails are treated; these may be better treated by another method.
 FIGURE 3-4. Liquid nitrogen as used for cryosurgery. (From Goodheart, H. P. 2010. Goodheart’s same-site differential diagnosis: A rapid method of diagnosing and treating common skin disorders. Philadelphia: Wolters Kluwer.) |
3. Few side effects, but can damage vital vessels and tear ducts; hyperpigmentation in darker skin is possible.
4. Application with cotton-tipped applicator allows for more control of tissue depth.
5. Blisters form in 3 to 6 hours after application, flatten in 2 to 3 days, and peel off in approximately 2 to 3 weeks.
6. If the site is kept clean, infection is rare.
PATIENT EDUCATION
