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Miscellaneous dermatology

Photosensitivity case study 1

A 64-year old Chinese market gardener presents in October with a one-month history of redness, dryness and swelling of his face, (as illustrated), V-of neck, backs of hands and forearms. He is otherwise well.

What external agents could have precipitated the rash? #! Contact irritants #! Contact allergens #! Aeroallergens #! Drug induced photosensitivity #! Idiopathic photosensitivity Explanation: The areas affected by the rash are exposed ie uncovered by clothing. You should consider all the suggested items.
  • Contact irritants could include dust, detergents and solvents. Read more about irritant contact dermatitis at DermNet.
  • Contact allergens could include fragrance, preservatives or sunscreen chemicals in cosmetics. Aeroallergens could include plant pollens and agricultural chemical sprays. Read more about allergic contact dermatitis at DermNet.
  • Drug induced or idiopathic photosensitivity. Read more about photosensitivity at DermNet.

The patient takes no medications and has not applied any creams to the affected areas. He wears fully protective clothing when using herbicides and pesticides.

A careful inspection of the rash reveals spared areas. It does not affect:

Which is more likely? * Contact allergic dermatitis *! Photosensitivity dermatitis * Atopic dermatitis * Contact irritant dermatitis Explanation: Photosensitivity dermatitis is more likely because contact dermatitis would be expected to involve all areas exposed to the allergen including furrows and creases.

The patient is treated with topical steroids, with minimal improvement. He is patch tested and photopatch tested. He has a positive contact allergic response to sesquiterpene lactone, which is the allergen associated with chrysanthemum allergy. He says he previously grew these flowers, but stopped doing so some years ago and is no longer exposed to them.

Read more about Chrysanthemum allergy at DermNet

Phototests are arranged.

Phototests are specialised tests that confirm: *! Abnormal sunburn reaction * The cause of photodermatitis * The best way to take a photograph * The skin fluoresces with exposure to longwave UVA Explanation: Phototests are specialized tests that confirm the presence of an abnormal sunburn reaction. Reduced minimal erythema doses to ultraviolet (UV) radiation (photosensitivity) may be due medications or to chronic photosensitivity dermatitis.

Phototests reveal markedly reduced minimal erythema doses to both UV-B and UV-A (illustrated). The diagnosis is chronic photosensitivity dermatitis. This disorder is more common in men and for unknown reasons is frequently associated with contact allergy to sesquiterpene lactone.

UVA is present outdoors throughout the day and throughout the year (although it is present in much greater quantities in the middle of the day and the middle of summer). Unlike UVB, UVA penetrates through normal window glass and is produced in low amounts by fluorescent lamps.

Management includes:

About 25% treated individuals go into remission within 10 years but the disorder persists for the remainder.

What measures might he take to protect his skin from sun exposure? Short answer:
  • Remain indoors during daylight hours
  • Clothing: broad brimmed hat, "Legionnaire's" style with flap at the back; long sleeves, long trousers, covering footwear, gloves
  • Broad spectrum sunscreen with physical blockers (zinc or titanium dioxide) applied liberally and frequently when outdoors
  • Perspex or fabric mask to protect facial skin outdoors during daylight hours (see illustration of a custom-made device)
  • Close curtains during the day or apply ultraviolet-blocking film to living area windows
  • Film should also be applied to vehicle windows
  • Change occupation to work indoors

Patients with chronic photosensitivity dermatitis are often severely disabled. In some cases, only a few seconds exposure to light is sufficient to cause dermatitis, which is unsightly and uncomfortable. Consider the impact on the patient: