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Wood’s light in dermatology

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dermatology ppt presentation

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Wood’s light in dermatology

  1. 1. By /Azza Samy
  2. 2. Introduction  A diagnostic method must be easy and quick to perform while delivering an accurate and consistent result.  An example of a diagnostic tool that meets these criteria is the Wood’s lamp.
  3. 3. Wood’s light physics  Wood’s lamp’s long-wave UV radiation (UVR) emission is generated by a high-pressure mercury arc fitted with a compounded filter made of barium silicate with 9% nickel oxide, the so-called ‘‘Wood’s filter.’’  This filter is opaque to all light except for a band between 320 and 400 nm with a peak at 365 nm.
  4. 4. Wood’s light physics(cont.)
  5. 5. Wood’s light physics(cont.)  A photon hitting the skin can be reflected away from the skin, scattered deeper into the skin, or absorbed by a molecule.  Fluorescence of tissue occurs when light of shorter wavelengths, in this case 340–400 nm, initially emitted by Wood’s light, is absorbed and radiation of longer wavelengths, usually visible light, is emitted.
  6. 6. Wood’s light physics(cont.)  The skin contains a plethora of fluorescent compounds, such as collagen, elastin, coenzymes and many others, which respond notably to UVA light.  If the skin is intact and not influenced by diseases or external factors: one can observe a bluish fluorescence due to these fluorophores.
  7. 7. Wood’s light physics(cont.)  In vitiligo, for example,diagnosis is confirmed by the lack of absorption by melanin residing in melanocytes or keratinocytes, resulting in bright bluish-white patches.  An exception is porphyria, in which there is an excess of fluorescent compounds in the skin, or skin infections caused by certain fungal or bacterial microorganisms that produce fluorescent chemicals.
  8. 8. Technique  Ideally, the lamp should be allowed to warm up for about 1 min.  Black occlusive shades or a windowless room are preferred.  It is also essential that the examiner becomes dark-adapted in order to see the contrasts clearly.  The lamp is held about 10-30cm from the lesion.
  9. 9. Considerations  Do not wash before the test, because that may cause a false-negative result.  Other materials may also glow. For example, some deodorants, make-ups, soaps, and even lint may be visible with the Wood's lamp.  Not all infections can be detected with the light. Some species of fungi and bacteria do not contain fluorescent chemicals
  10. 10. Practical applications
  11. 11. Practical applications (Pigment disorders)  In hypopigmented or depigmented lesions,  There is less or no epidermal melanin. Consequently, there is a window through which the Wood’s light- induced autofluorescence of dermal collagen can be seen. The lesions appear bright blue–white due to autofluorescence.
  12. 12. Pigment disorders(cont.)  In hyperpigmented lesions, When incident light impinges upon the skin, photons of shorter wavelengths, especially UVB (290–320 nm) and UVA (320–400 nm), are more easily scattered by the stratum corneum and the epidermis.  Contrarily, photons of longer wavelengths, such as the visible range (400–800 nm), penetrate more deeply into the dermis.
  13. 13. Pigment disorders(cont.) Melanin absorbs light very strongly in both the UV and visible regions. When Wood’s light is illuminated over a heavily melanized epidermis, most of its output is absorbed, while the less darkly pigmented adjacent skin scatters and reflects light as usual, resulting in enhanced contrasts at the border zone between areas of differing melanization.
  14. 14. Pigment disorders(cont.)  Variations in epidermal pigmentation thus become more apparent under Wood’s light than under ordinary room light.  For dermal pigmentation, this contrast is less apparent under Wood’s light because some of the autofluorescence of the dermal collagen takes place both above and below the dermal melanin, which serves to diminish the amount of fluorescence returned to the eyes.
  15. 15. Melasma  Melasma is a common hyperpigmentary disorder of the skin caused by an overproduction of pigment on sun exposed areas, mainly the face, which results in hyperpigmented patches.  In melasma, the hyperpigmentation can be epidermal, dermal or mixed.  Melasma is treated with depigmenting creams or with other methods such as laser and IPL therapy.
  16. 16. Melasma(cont.)  In this treatment, mainly the epidermal pigment responds.  The Wood’s lamp is not only beneficial to confirm diagnosis; in addition, it can distinguish whether the hyperpigmentation is epidermal, dermal or mixed and there by determine whether therapy is effective or not.
  17. 17.  Epidermal-type melasma shows enhancement of color contrast when examined under Wood’s light as compared to visible light.  Conversely, melasma of dermal type, which may have a slight bluish hue in natural sunlight, does not demonstrate such contrast enhancement when seen under Wood’s light.
  18. 18.  Patients with mixed-type melasma showed color enhancement in some areas, but not in others.  Melasma in patients with darker complexions (skin types V and VI) was more evident in visible light than under UV light, hence the Wood’s light inapparent type.
  19. 19. Comparison between photography with visible light (top) and with the use of Wood's lamp (bottom) highlighting the limits of the frontal macules of melasma .
  20. 20. Vitiligo  Vitiligo is a disease in which skin and hair lose their melanocytes resulting in depigmented patches on the skin,varying in size and shape.  The Wood’s lamp can be used to confirm diagnosis when vitiligo is suspected. Furthermore, it allows to distinguish vitiligo from an anaemic naevus, pityriasis versicolor and pityriasis alba.
  21. 21.  In vitiligo, because of loss of epidermal melanin, depigmented patches appear bright bluish-white with sharp demarcations in the Wood’s light.  In contrast, an anaemic naevus, caused by local dermal vasoconstriction with normal overlying epidermal pigment, does not show up in the Wood’s light.
  22. 22.  In pityriasis versicolor, the yeast causing the skin disorder gives a yellowgold fluorescence.  Finally, pityriasis alba, with irregular parakeratosis and little melanocyte activity, is not noticed in the Wood’s light.  Follicular repigmentation following oral photochemotherapy can be demonstrated earliest by the use of Wood’s light.
  23. 23. Vitiligo: bright bluish-white fluorescence in Wood’s light.
  24. 24. Progressive macular hypomelanosis  PMH is a pigment disorder with non-itching, non- scaly, hypopigmented macules, mainly localized on the trunk.  Westerhof found a relation between PMH and Propionbacterium acnes.
  25. 25. Progressive macular hypomelanosis (cont.)  Examination of PMH with the Wood’s lamp showed bright bluish-white fluorescence of the skin lesions due to the lack of melanin, as well as follicle-bound coral-red fluorescence due to coproporfyrine III.  Coproporfyrine III is a chromophore produced by Propionbacterium acnes
  26. 26. Progressive macular hypomelanosis (cont.) Progressive macular hypomelanosis: bright bluish-white lesions and follicle-bound coral-red fluorescence.
  27. 27. Tuberous sclerosis  An ‘ash-leaf’ macule is a leaf-shaped, hypopigmented macule, a characteristic of tuberous sclerosis.  On a light skin type, this lesion can be hard to see but easily detected with the Wood’s lamp.  Finding these lesions early on allows dermatologists to alert primary care physicians as to possible seizures or other clinical problems.
  28. 28. Tuberous sclerosis(cont.) An ‘ash-leaf’ macule easily detected with the Wood’s lamp.
  29. 29. Infections of the skin ((Fungi and yeasts  Fungi and yeasts cause dermatomycoses of skin, hair and nails. Fungi are divided into three different strains, Microspora, Trichophyton and Epidermophyte species.  The Microspora species produce a metabolite, pteridine, which fluoresces bright-green if illuminated by the Wood’s lamp .
  30. 30. Tinea capitis  Tinea capitis is a trichomycosis often caused by Microspora species.  When tinea capitis is suspected, the diagnosis can be directly confirmed using the Wood’s lamp .  However, tinea capitis can also be caused by a Trichophyton species, which does not fluoresce. That is why a lack of fluorescence can never exclude tinea capitis.
  31. 31. Tinea capitis(cont.)  One exception in the Trichophyton species, Trichophyton schoenleinii the cause of favus, causes yellowish, cup-shaped crusts, grouped in patches like a piece of honeycomb. In the Wood’s light, it causes a blue fluorescence.
  32. 32. Tinea capitis caused by Microsporum: bright-green fluorescence.
  33. 33. Tinea manuum: bright-green fluorescence in Wood’s light.
  34. 34. Pityriasis versicolor  Pityriasis versicolor is a superficial fungal infection of the skin caused by Malassezia furfur, a spore- forming yeast.  Infected lesions fluoresce yellow-gold, also described as chamois leather.
  35. 35. p. versicolor under Wood's lamp
  36. 36. Pityrosporum folliculitis  Pityrosporum folliculitis is caused by the same yeast as pityriasis versicolor and is therefore also seen as its local or follicular form.  Overgrowth of Malassezia furfur causes follicular erythematous papules and pustules, sometimes itching and mainly localized on chest and upper back.  When illuminated by the Wood’s light, a follicular pattern of bluish-white fluorescence is seen, which allows for a clear distinction between pityrosporum folliculitis and a bacterial folliculitis.
  37. 37. Bacterial infections ((Propionbacterium acnes  Propionbacterium acnes produces coproporphyrin III and protoporphyrin IX, in the Wood’s light these chromophores show an orange-red fluorescence.  On the facial skin, the Wood’s lamp highlights an orange-red fluorescence from comedones.
  38. 38. Propionbacterium acnes in comedones: follicle- bound coral-red fluorescence.
  39. 39. Pseudomonas infection  The Wood’s lamp can also be used to detect Pseudomonas infections of the skin, for example, in burns or toe web infections.  Pseudomonas bacteria excrete a pigment, pyoverdin, which fluoresces yellowish-green in the Wood’s light.
  40. 40. Pseudomonas infection(cont.)  The Wood’s lamp can be used as an early diagnostic tool to detect Pseudomonas infection of burns or other wounds, long before Pseudomonas shows up in a bacterial culture, allowing to start the right treatment at an early stage.
  41. 41. Pseudomonas infection: yellow-green fluorescence in Wood’s light.
  42. 42. Erythrasma  Erythrasma is a skin infection caused by overgrowth of Corynebacterium minutissimum.  It occurs in body folds and causes a scaly, red-brown discoloration of the skin and an itching or burning sensation.
  43. 43. Erythrasma(cont.)  Corynebacterium minutissimum produces coproprophyrine III, which causes a coral-red fluorescence when illuminated by Wood’s light.  Because of the coralred fluorescence, the Wood’s lamp is a direct diagnostic tool to distinguish erythrasma from intertrigo, tinea inguinalis or psoriasis inversa.
  44. 44. Erythrasma: coral-red fluorescence in Wood’s light.
  45. 45. Porphyria  Porphyria is a metabolic disorder caused by an enzymatic disturbance in the biosynthesis of haem.  Because of a lack of haem, porphyrins accumulate.  Due to an excess of porphyrin metabolites, sensitivity to light occurs, which can manifest clinically in various forms.
  46. 46. Porphyria(cont.)  Porphyrin fluoresces pink-red in the Wood’s light.  Depending on the type of porphyria, accumulation can be noted in urine, faeces, erythrocytes or teeth.
  47. 47. Characteristic fluorescence observed in the principal porphyrias
  48. 48. congenital erythropoietic porphyria - teeth: red on woods lamp
  49. 49. Porphyria Cutanea Tarda: urine flouresces pink red
  50. 50. Tumours (Photodynamic diagnosis)  Based on the fact that δ-ALA-derived porphyrins preferentially accumulate in neoplastic tissues, Fritsch et al. reported the use of topical δ-ALA and Wood’s lamp to delineate the margin of recurrent basal cell carcinomas.  20% ALA ointment was applied to the tumor and left on for 4–6 h under occlusion allowing protoporphyrinogen IX to accumulate, after which the area was illuminated withWood’s light.
  51. 51. Tumours (Photodynamic diagnosis)  The tumor emitted bright-red fluorescence.  These fluorescence positive areas proved to be basal cell carcinomas on histologic examination.  This photodynamic diagnosis has proved useful in other conditions, including solar keratosis, Bowen’s disease, squamous cell carcinoma, and extramammary Paget’s disease.
  52. 52. Tumours (Photodynamic diagnosis)  This technique, when perfected, will be of great help to physicians taking care of skin cancers.  It seems likely that additional specific, noninvasive, and useful optical techniques will be developed in the next decade.
  53. 53. THANK YOU

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