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Chapter 9: Photodermatoses

CHONG Wei Sheng; NOOR HANIF bin Said; TAN Wei Min Aaron

INTRODUCTION

Photodermatoses are a broad group of skin disorders primarily caused or exacerbated by exposure to ultraviolet radiation (UVR) or visible light (VIS). Photodermatoses can be classified into several categories:

  1. Immunologically-mediated

  2. Exogenous agents (drugs and chemicals)

  3. Metabolic and genetic disorders

  4. Photoaggravated dermatoses

The management of photodermatoses starts with the clinical recognition of lesions that are predominantly evident on sun-exposed skin including the forehead, bridge of nose, upper cheeks, rims of ears, back and sides of neck, upper chest, dorsa of hands and feet, and extensor aspects of arms and lower legs. Areas spared include those beneath the hair fringe, upper eyelids, below the nose, upper lip, behind the earlobes, and web spaces of the fingers. A systematic approach including pertinent history, physical examination, relevant laboratory investigations, and confirmatory photodiagnostic tests (e.g., phototest, photoprovocation test, photopatch test) are essential steps in patient evaluation.

At our center, photoaggravated dermatoses and the immunologically-mediated photodermatoses account for two-thirds of patients seen for the evaluation of photosensitivity. Immunologically-mediated photodermatoses are being increasingly diagnosed locally. This may reflect an increase in recreational and military-related sun exposure with inadequate sunscreen use. Familiarity with the more common photodermatoses seen here and their variations will aid in the diagnosis and management of such patients. With the identification of common phototoxic drugs and photoallergens, it is also hoped that drug and chemical-induced photosensitivity will be reduced or more promptly recognized and addressed.

IMMUNOLOGICALLY-MEDIATED PHOTOSENSITIVITY

Polymorphic light eruption

Polymorphic light eruption (PMLE), as in other parts of the world, is the most common acquired immunologically-mediated photosensitivity disorder seen (Figures 9–1, 9–2, 9–3, 9–4, 9–5, 9–6). Papules, papulovesicles, and plaques evident on the sun-exposed skin are the predominant features, and pruritus is a common symptom. A lichen nitidus-like morphological variant (pinpoint papular PMLE) occurs in darker-skinned Asians of Fitzpatrick skin types IV to VI, which is uncommon in Caucasians.

Figure 9-1

Polymorphic light eruption—papules and plaques

Multiple erythematous papules and plaques are seen on the sun-exposed areas of the forearms of this male patient. This papular-plaque variant is the commonest morphology seen, and the distribution is usually patchy. The lesions typically erupt hours after sun exposure and resolve within a few days to two weeks without scarring.

A patient with polymorphic light eruption exhibits several small, red, papular plaques covering the forearms.
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Figure 9-2

Polymorphic light eruption—pinpoint papular variant

Multiple tiny, pinpoint, shiny, hypopigmented papules are seen over the dorsal hands of this patient. These papules resemble lesions of lichen nitidus. This variant is not uncommon in Asian skin, and shows a predilection for darker-skinned Chinese, Malays, and Indians. In the West, it has been reported only in African-Americans. It often resolves with post-inflammatory hypopigmentation. The pin-point papular variant of polymorphic light eruption, unlike lichen nitidus, is usually pruritic and confined to sun-exposed areas.

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