microscopic examination of scales, crusts, serum and hair
1- microscopical examination for fungus infection.
the highest rate of recovery of organisms occurs in specimens taken from the tops of vesicles and the active edges of a lesion. the site should be swabbed with an alcohol pad or water and scraped with a # 15 blade, or the roofs of vesicles are snipped off with scissors. the moist corneocytes are then easily transferred from the blade to a glass slide. one or two dropings of 10-20% aqueous potassium hydroxide solution added to the specimen and covered with a cover slip and left 30 minutes to clear or gently warmed but not boiled. it is then examined under the light microscope with the 8mm or 4mm objective using low illumination. the mycelia are recognized as branching refractile threads which boldly transgress the outlines of the squamous cells. (fig.12).
fig.12. the mycelia are recognized as branching refractile threads
nails are examined in much the same way but it is necessary to break up the snippings and shavings into small fragments. these are either heated in potassium hydroxide or are left to clear in it overnight before being examined.
a scalp lesion is cleaned with 70% alcohol or with 1% cetrimide. infected stumps and scales are removed by scraping with a scalped and put on glass slide. the infected hairs are cleaned in potassium hydroxide in the same way as skin scales. examination under the microscope reveals spores on the outside of the hair roots, and mycelia inside the hair substances. the confirmation of the diagnosis and the species of fungus responsible can be established by culture on dermatophyte test media or sabouraud’s dextrose agar (with or without antibiotics and cyclohexamide that added to suppress bacterial contaminants and yeasts). the easily broken infected hairs are embedded in the culture media in which two weeks or more are needed for the fungus to grow.
2-gram stains and cultures of exudates and of tissue minces should be made in lesions suspected of being bacterial or yeast (candida albicans) infections. ulcers and nodules requires a scalped biopsy in which a wedge of tissue consisting of all three layers of skin is obtained the biopsy specimen is put in a sterile tube and is then cultured for bacteria (including typical and a typical mycobacterium) and fungi in a specific media accordingly.
3-microscopic examination of cells obtained from the base of vesicles (t zanck preparation) may reveal the presence of acantholytic cells in the acantholytic diseases (e g. pemphigus or sss syndrome) or of giant epithelial cells and multinucleated giant cells (containing nuclei) in herpes simplex, herpes zoster, and chicken pox.
an intact vesicle (blister) is opened along one side, the roof folded back, and the underside gently scraped. the material obtained by gentle curettage with a scalpel is smeared on a glass slide, allowed to air-dry, and stained with either sedi-stain, giemsa’s stain, wright’s stain or methylene blue, and examined to determine whether there are acantholytic (which are rounded with either cytoplasmic contents at the periphery in pemphigus vulgaris (fig.13 ). or giant epithelial cells (show typical multinucleated giant cells of herpes simplex) (fig.14). culture of herpes simplex is now easily available.
fig.13. acantholytic cells fig.14. giant epithelial cells of
of pemphigus vulgaris. herpes simplex.
4-laboratory diagnosis of scabies
the diagnosis of scabies is usually considered clinically in a patient with sever intractable generalized itching with the skin rash in the form of papules or papulo-vesicles and excoriations distributed in characteristic locations on the flexor aspects of the wrists in the finger webs, anterior axilla areola of breast in female, and on the buttocks and genitalia (fig.15 ), the diagnosis is established by identification of the mite, or ova or feces, in skin scrapings removed from the papulovesicles or burrows (see fig.16). the burrow, a unique lesion, is a linear or serpiginous elevation of skin in the form of a ridge, 0.5 to 1.0 cm in length. these occur on the anterior surface of the wrists, in the webs of the fingers, or on the ulnor border of the hand. if burrows are not present, select a papule or the roof of a vesicle on the hand. the mineral oil technique is excellent for isolating the mite. using sterile scalped blade on which a droping of sterile mineral oil has been placed, apply oil to the surface of the burrow or papule. scrape the papule or burrow vigorously (about six times) in order to remove the entire top of the papule tiny flecks of blood will appear in the oil. transfer the oil to a microscopic slide and examine for mites, ova and feces. the mites are 0.2 to 0.4mm in size and had four pairs of legs (see fig.17, 18).
fig.15 scabies fig.16 burrows with sarcopets
scabiei (female), eggs and feces
fig.17sarcopets scabiei female. fig.18 scabies. characteristic linear
burrows in a typical location.
5-skin biopsy
biopsy (from the greek bios meaning ‘life’ and opsis ‘sight’) of skin lesions is useful to establish or confirm a clinical diagnosis. a piece of tissue is removed surgically for (histopathology, immunofluorescence, electron microscopy) and some tissues for other tests (e g. culture for organisms). when used selectively, a skin biopsy can solve the most perplexing problem but, conversely, will be unhelpful in conditions without a specific histology (e g. most drug eruptions, pityriasis rosea, reactive erythema). selection of the site of the biopsy is based primarily on the stage of the eruption and early lesions are usually more typical this is especially important in vesiculo-bullous eruptions (e g. pemphigus, herpes simplex), in which the lesion should be no more than 24hours old. however, older lesions (2 to 6 weeks) are often more characteristic in discoid lupus erythematosus.
there are many types of skin biopsy:
· punch biopsy: a small tubular knife is used to remove 3.0 to 4.0mm cuts of epidermis and subcutaneous tissue in a cork screw movements between the thumb and index finger (fig.19), then the base is cut off with scissors.
fig. 19 punch biopsy
· incisional biopsy: when just part of a lesion is removed for laboratory examination or
· excisional when the whole lesion is cut out especially when the lesions are small (up to 0.5cm diameter) but incisional biopsy is chosen when the partial removed of a larger lesion is adequate for diagnosis, and complex removed might leave an unnecessary and unsightly scar. ideally, an incisional biopsy should include a piece of the surrounding normal skin specimen. for light microscopy should be fixed immediately in buffered neutral formalin, label the specimen container with patient’s name, age, sex, site of the biopsy and the time is taken. provide the pathologist with detailed summary of the clinical history, description of the lesions and differential diagnosis and better to discus the results with the pathologist.
· shave biopsy: indicated in -benign superficial epidermal lesions e.g. seborrhoeric keratosis, actinic keratosis. – benign intradermal naevi may be partially removed ? fig.20 ?.
fig. 20 shave biopsy
المادة المعروضة اعلاه هي مدخل الى المحاضرة المرفوعة بواسطة استاذ(ة) المادة . وقد تبدو لك غير متكاملة . حيث يضع استاذ المادة في بعض الاحيان فقط الجزء الاول من المحاضرة من اجل الاطلاع على ما ستقوم بتحميله لاحقا . في نظام التعليم الالكتروني نوفر هذه الخدمة لكي نبقيك على اطلاع حول محتوى الملف الذي ستقوم بتحميله .