Photodermatology Overview & Porphyrias Flashcards
List the benefits & hazards of ultraviolet radiation (UVR)
Benefits:
- Photosynthesis
- Vitamin D synthesis
- Heat
- Vision
- Circadian rhythms
- Bactericidal
- Therapeutic & diagnostic use
Hazards:
- Sunburn
- Eyes - conjunctivitis, keratitis, cataract
- Skin cancer
- Photoageing
- Photosensitivity - photodermatoses
List the different sources of UVR
- Solar
- Artificial; Therapeutic or Sunbeds
Give examples of the theraputic uses of UVR
Phototherapy:
- UVB: narrow band largely replaced broad band
- UVA: new developments eg. eczema
Photochemotherapy:
- Psoralen + UVA = PUVA
What is the fitzpatrick scale ?
The Fitzpatrick is a numerical classification schem for human skin colour developed as a way to estimate the response of different skin types to UV light.
- Type I only burns, never tans (pale white; blond or red hair; blue eyes; freckles).
- Type II usually burns, tans minimally (white; fair; blond or red hair; blue, green, or hazel eyes)
- Type III tans, can burn (cream white; fair with any hair or eye color)
- Type IV always tans, burn minimally (moderate brown)
- Type V very rarely burns, tans very easily (dark brown)
- Type VI Never burns, never tans (black skin)
What are the chronic effects of UVR exposure?
- Cumulative exposure greatest link to causing SCC (more so than BCC)
- Acute sunburns: melanoma
Define what is meant by photosensitivity
Photosensitivity refers to various symptoms, diseases and conditions caused or aggravated by exposure to sunlight.
Define what is meant by the term photodermatosis (plural photodermatoses)
This is the terms used to describe a rash due to photosensitivity
In general what are the clinical features of photosensitivity ?
- The clinical features depend on the specific photodermatosis.
- Photodermatoses affect areas exposed to sunlight (face, neck, hands) and do not affect areas not exposed to the light (covered at least by underwear), or are less severe in covered areas.
In general how are photosensitivity conditions diagnosed ?
Photosensitivity is diagnosed by the history of a skin problem arising on exposure to sunlight. The specific type is determined by examination of the skin and specific tests:
Photosensitivity is sometimes confirmed by phototests e.g. MED test, provocation test & Monochromator phototesting
Contact photosensitivity can be tested by photopatch tests, in association with standard patch tests.
Investigations may include:
- FBC
- Connective tissue antibodies including ANA & ENA antibodies
- Porphyrins in blood, urine and faeces
What is done in phototests ?
Artificial light from various different sources and at different doses is shone on small areas of the skin to see whether the rash can be reproduced, or if sunburn occurs more easily than expected.
What is done in photopatch tests ?
Adhesive patches containing known photosensitising materials are applied to the upper back, removed after two days, and light is shone on the area. The reaction is observed two days later.
In general how are photosensitivities treated?
- Management of photosensitivity involves sun protection and treatment of the underlying disorder.
- Theraputic UVR exposure may be used to harden the skin to sun exposure
List the 4 main categories of photodermatoses
- Immunological
- Genetic
- Chemical photosensitivity - Exogenous (eg drugs), Endogenous (eg porphyria)
- Photoaggravated dermatoses
List the immunological photodermatoses
- Polymorphic light eruption
- Actinic prurigo
- Solar urticaria
- Chronic actinic dermatitis
- Hydroa vacciniforme
Define what is meant by cutaneous photosensitivity
Photosensitivity refers to any increase in the reactivity of the skin to sunlight resulting in an abnormal reaction.
What are some of the different treatment options for cutaneous photosensitivity
- Behavioural avoidance
- Sunscreen
- Hardening phototherapy (using UV light, hardening induces better tolerance of the skin)
- Chormophore (e.g. melanin in hair, or oxyhemoglobin in blood vessels) removal
- Inhibition of mediator/action release
- Inhibition of inflam response
What is a porphyria ?
A rare hereditary disease in which there is abnormal metabolism of the blood pigment haemoglobin. Porphyrins are excreted in the urine, which becomes dark; other symptoms include mental disturbances and extreme sensitivity of the skin to light.
Appreciate the biochem of porphyrias
What are the 4 main groups of porphyrias ?
- Phototoxic skin porphyrias (such as erythropoietic protoporphyria)
- Blistering and fragility skin porphyrias
- Acute attack porphyrias (some with no skin involvement; some also cause blistering and fragility)
- Severe congenital porphyrias (such as congenital erythropoetic porphyria)
What are some of the common skin porphyria features ?
Blistering/fragility and acute phototoxic
What is Porphyria cutanea tarda and what in terms of biochemistry causes it ?
This disease is the most common of the porphyrias and results from a deficiency of the enzyme uroporphyrinogen decarboxylase (UROD) which is involved in the synthesis of the red pigment in blood cells (haem).
What are the two different classes of PCT?
Type I and Type II
Describe Type I PCT
Type 1 PCT generally begins in mid-adult life after exposure to certain chemicals that increase the production of porphyrins (precursors of haem) in the liver. These include:
- alcohol
- oestrogen eg oral contraceptive, hormone replacement or liver disease
- polychlorinated aromatic hydrocarbons (e.g. dioxins, when PCT is associated with chloracne).
- iron overload, due to excessive intake (orally or by blood transfusion), viral infections (hepatitis, especially hepatitis C) or chronic blood disorders such as thalassaemia (acquired haemochromatosis), or hereditary haemochromatosis
Describe type II PCT
Type 2 PCT is familial and associated with abnormal genetic variants of uroporphyrinogen decarboxylase. Trigger factors are less often involved and onset of PCT is often younger than in type 1 PCT.
What is the clinical presentation of porphyria cutanea tarda ?
People present with increasingly fragile skin on the back of the hands and the forearms. Features include:
- Sores (erosions) following relatively minor injuries
- Fluid filled blisters (vesicles and bullae)
- Tiny cysts (milia) arising as the blisters heal
- Increased sensitivity to the sun
Mottled brown patches around the eyes and increased facial hair (hypertrichosis) & hyperpigmentation.
Characteristically, the urine is darker than usual, with a reddish or tea-coloured hue.
What feature is shown here ?
Morphea (painless discoloured patches) - sign of PCT
What feature is shown here and what condition is it linked to ?
Hyperpigmentation - linked to PCT
Name the feature and the condition this feature is linked to ?
Solar urticaria - linked to PCT
What is PCT associated with ?
Abnormal LFTs & iron overload
How is PCT diagnosed ?
- Skin biopsy : characteristic changes are seen which differentiates PCT from other blistering diseases.
- urine: elevated uroporphyrinogen (shown on 24hr urine porphyrin profile) and urine appears pink fluorescence under Wood’s lamp
- serum iron ferritin level is used to guide therapy
What are the clinical features of erythropoietic protoporphyria ?
- Usually starts in childhood as an uncomfortable or painful burning sensation of the skin after sun exposure - kids may start to cry when taken out into sunlight etc.
- The affected skin may become red and swollen and blistered.
- Later there are pitted scars and sometimes crusty thickened skin, particularly over the cheeks, nose and knuckles of the hand
- It occurs most often on the tops of the hands and feet, face and ears.
What is the feature shown here and what condition is it linked to ?
Cheek scars (scars on sun-exposed areas of skin) - Erythropoietic protoporphyria
What are the clinical features of PLE?
It may be a rare occurrence or may occur every time the skin is exposed to sunlight. The features include:
- Presents as crops of 2-5mm papules usually, but sometimes vesciles (blisters)
- The papules persist for several days and then resolve without scarring
What are the clinical features of actinic prurigo?
- Characterised by an intensley itchy rash appearing hrs or days following sun exposure
- The rash consists of an eruption of small, scratched, red and inflamed papules, thickened plaques, and nodules. (looks a lot like eczema)
- Sun-exposed areas of the face such as the cheeks, nose, forehead, chin and earlobes. V of the neck and chest, upper sides of the arms and hands are affected
What are the clinical features of solar uritcaria ?
- A stinging, itchy rash develops within minutes after a short period (less than 30 minutes) of sun exposure.
- The rash may look like weals and be red and swollen
What are the clinical features of chronic actinic dermatitis ?
- The lesions are usually red and inflamed with scaling and lichenification (thickened and hardened patches of skin).
- The rash can be very itchy.
What are the clinical features of hydroa vacciniforme ?
In most cases signs and symptoms usually start to occur about 30 minutes to 2 hours after sun exposure and present as:
- Mild burning, itching or stinging
- Development of tense, swollen bumps (papules) and blisters (vesicles); there may be facial swelling
- These turn into dimpled, pit-like papules with black scabs (necrosis) on a red and inflamed base
- Lesions heal to form pale depressed scars
What are the clinical features of xeroderma pigmentosum?
The disease usually progresses through 3 stages. The first stage occurs around 6 months after birth (skin appears normal at birth):
- Areas exposed to the sun such as the face show reddening of the skin with scaling and freckling. Irregular dark spots may also begin to appear. These skin changes progress to the neck and lower legs.
Continued sun exposure will lead to the second stage, which is characterised by:
- Poikiloderma
- Skin atrophy
- Telangiectasia
- Mottled hyperpigmentation and hypopigmentation.
The 3rd stage is the development of actinic keratoses and skin cancers. They include:
- Basal cell carcinoma
- Squamous cell carcinoma
- Melanoma.
Eye problems occur in nearly 80% of xeroderma pigmentosum patients.
Eyes become painfully sensitive to the sun (photophobia), easily irritated, bloodshot and clouded. Conjunctivitis may occur. Non-cancerous and cancerous growths on the eyes may occur.
