Definition

Photosensitivity is an abnormal skin response involving the interaction between photosensitizing substances and sunlight or filtered or artificial light at wavelengths of 280-400 nm. There are two main types: photoallergy & phototoxicity.

How does it present?

The abnormal skin response can be the development of a skin rash, an exacerbation of an existing rash, an exaggerated sunburn or symptoms such as pruritus (itchy skin) or paraesthesia (burning) after exposure to the light.

Prevalence

Photosensitivity is common and probably affects members of all racial and ethnic groups, although there has been no studies of its prevalence in the general population.

Types of Photosensitivity

Acute Photosensitivity

• Polymorphous Light Eruption
  (PLE) is the most common cause of acute or episodic photosensitivity. It probably accounts for more than 90% of all cases. PLE was found to have a prevalence of 10% in a survey of 271 apparently healthy people in Boston. In other studies it was diagnosed in 21% in Sweden, 14% in London & 5% in Perth, Australia. There is a broad spectrum of disease in PLE. People who have a mild form of the disease never consult a doctor.
  PLE is a recurrent condition that persists for many years in most patients.
  It presents as papular (bumps) or papulovesicular (small water blisters) eruption within hours or days after exposure to the sun, lasting for days to a week or more. It affects females more than males (3:1), age range commonly between 20-40 yr.
  Treatment is with topical or oral steroids for acute rash and sunscreens, avoidance or desensitization for prevention.
• Subacute Cutaneous Lupus Erythematosus (SCLE) also affects females more than males (2:1) and similar age range as PLE (20 – 40 yr).
  It presents as annular (shaped like a ring), polycyclic, psoriasiform (scaly rash looking like psoriasis) eruption within days after exposure to the sun and lasting for weeks.
  It is treated with topical or oral steroids for the acute rash; sunscreen, sun avoidance and antimalarial drugs for prevention.
• Solar Urticaria is rare. It affects the sexes equally and usually the same age group as above (20 -40 yr).
  It presents as itching & hives (urticaria) within minutes of exposure to the sun and lasts for hours.
  It is treated with antihistamines and desensitization with phototherapy.
• Photoallergy is also rare & affects the sexes equally. It can affect any age.
  It presents as eczema on the exposed areas.
  It is diagnosed with a Patch Test and treated by stopping the topical agent causing it. Steroids are also used to supress the inflammation.
• Drug-induced Phototoxicity.
  It presents as an exaggerated sunburn hours to days after exposure to sun, lasting for days to a week.

Drugs likely to cause Photosensitivity

Antidepressants
Clomipramine (Anafranil)
Sertaline (Zoloft)
Tricyclics: Elavil, Asendin, Tofranil, Surmontil

Antihistamines
Astemizole (Hismanal)
Cetirizine (Zyrtec, Razene)
Cyproheptadine (Periactin)
Dimenhydrinate (Dramamine)
Diphenhydramine (Benadryl)
Hydroxazine (Atarax)
Loratidine (Claratyne, Lora-tab)
Phenergan
Trefanidine (Teldane)

Cancer Chemotherapy
Fluoracil (5-FU)
Methotrexate
Vinblastine

Cardiovascular
ACE-inhibitor: Captopril, Accupril, Univasc
Amiodarone
Beta- Blockers: Sotalol
Calcium Chanel Blockers: Diltiazem, Nifedipine
Disopyramide (Norpace)
Lipid Lowering: Simvastatin (Zocor)

Coal Tar & derivatives
Pinetarsol

Prevention of Drug Photosensitization

Patients taking medication that are likely to cause photosensitivity should minimise exposure to sunlight & use broad-spectrum sunscreens & protective clothing. Once daily medication should be taken in the evening.

Chronic Photosensitivity

Chronic photosensitivity appears to be much less common than acute photosensitivity. The prevalence is uncertain, as it is probably under-diagnosed, because patients are often unaware that a skin eruption is caused by sunlight.

The eruption is usually present year-round, but sometimes it is present only in warm months. Exposure to sunlight could exacerbate the eruption or may produce little change. The key point to the diagnosis is that the rash is mainly confined to exposed skin.

Types of Chronic Photosensitivity

• Chronic Actinic Dermatitis is rare. It mainly affects men over the age of 60 yrs.
  It presents with eczema on exposed areas year-round or mainly in the summer.
  It is treated with Sun avoidance or desensitization with phototherapy or immune suppressive drugs.
• Actinic Prurigo is rare and affects the sexes equally. It affects any age.
  It presents with intensely itchy papules (bumps) & nodules (larger bumps), often with inflamed lips & scarring.
  It is treated with sun avoidance & desensitisation with phototherapy
• Photoexacerbated atopic eczema mainly affects females at any age.
  It presents with eczema on exposed areas. There is usually a history of flexural eczema and possibly Hay fever and asthma.
  It is treated with sun avoidance & desensitization with phototherapy.
• Porphyra cutanea tarda is a rare form of photosensitivity affecting mainly adult males.
  It presents with erosions (sores) & bullae (blisters) after minor trauma, mainly on the backs of the hands & forearms.
  It is diagnosed by measuring urinary porphyrins & treated by venesection & chloroquine.
• Systemic lupus erythematosus (SLE) & dermatomyositis affects mainly adult females.
  It presents with minor photosensitivity (rash in the malar area of the face), prominent systemic symptoms.
  It is treated with sun avoidance & Antimalarials