SKIN DISEASE IN PORPHYRIA
Though the acute attack constitutes
the most dangerous complication
of porphyria, it is porphyrin skin
disease which is by far the commonest
presentation.
PORPHYRIAS ASSOCIATED WITH SKIN
DISEASE
Both variegate porphyria
(Read Variegate
porphyria), the common South
African form of porphyria, and porphyria
cutanea tarda (Read Porphyria
cutanea tarda) are commonly
accompanied by skin disease. Skin
disease is also encountered in hereditary
coproporphyria and in congenital
erythropoietic porphyria (Read Unusual
forms of porphyria).
CLINICAL DESCRIPTION
 Porphyric
skin disease has a characteristic
appearance. Lesions are found only
in sun-exposed areas: typically
the backs of the hands, the forearms
and to a lesser extent, the back
of the neck and the feet in people
who wear open shoes or sandals.
In the acute setting, lesions consist
of fluid-filled blisters and small
erosions (Click on the images).
Typically these are few in number,
with only 3 or 4 small fresh lesions
at any time. A common associated
finding are milia: pinpoint deposits
of a whitish, waxy material within
the skin. Chronic appearances in
most cases consist of small marks,
the residue of the acute lesions,
which tend to be either lighter
or darker than surrounding skin.
These may persist for months or
years, gradually fading as time
passes. In most cases of variegate
porphyria and porphyria cutanea
tarda, skin disease is fairly subtle.
Photomutilation
 Severe
skin disease is a feature of untreated
porphyria cutanea tarda and of the
exceedingly rare disorders congenital
erythropoietic porphyria (See Unusual
forms of porphyria) and the
homozygous forms of variegate porphyria
and porphyria cutanea tarda (also
known as hepatoerythropoietic porphyria).
In these disorders, the skin in
sun-exposed areas becomes increasingly
disfigured with pigmented blotches,
coarsening and premature aging of
the skin, hypertrichosis and eventually
photomutilation with sclerodactyly
and contraction and ultimately loss
of appendages such as eyelids, nose,
ears and lips.
The image on the
left shows the hands of a ten-year
old child with homozygous variegate
porphyria: note the chronic skin
damage and mutilating changes in
the fingers.
PATHOGENESIS
The phenomenon of
fluorescence
Porphyrin molecules
exhibit the property of fluorescence.
Light is absorbed at ultraviolet
wavelengths centred around 406 nm.
The trapped energy promotes electrons
to a higher-energy state. As the
electrons subsequently relax to
the low-energy state, they re-radiate
the additional energy at red wavelengths-typically
about 630 nm. It is believed that
these energy fluxes, occurring within
the skin, underlie the photodermatitis
characteristic of the porphyrias.
There are thus two factors necessary
for the pathogenesis of the skin
lesions: excess porphyrins within
the skin, and exposure to light.
Frequently a third factor—trauma—is
present: it is often noted that
the skin breaks easily after minor
trauma such as knocks and scrapes,
and then heals unusually slowly.
Ultraviolet light
and photosensitivity
Not all wavelengths
of light have the same damaging
effect on the skin. It is principally
the long-wavelength ultraviolet
light (UVA), of wavelength approaching
400 nm, that is most damaging. Note
that these wavelengths are considerably
longer than those which cause sunburn—UVB.
Even longer wavelengths, in the
visible spectrum, can be damaging
in porphyria. This has important
consequences for the prevention
of porphyrin skin disease: conventional
sunblocks, which screen out UVB
rather than UVA, are unhelpful in
preventing porphyric skin damage.
PORPHYRIA CUTANEA TARDA
 The
skin disease of porphyria cutanea
tarda (Read Porphyria
cutanea tarda) is similar to
that of variegate porphyria, and
in milder cases the two cannot be
distinguished clinically. In some
cases of porphyria cutanea tarda
the skin disease is more severe,
with large, ugly blisters and open
sores on the hands and face , darkening
and coarsening of the skin, hypertrichosis
and sclerodactyly. Thickening and
tightening of the skin of the face
and hands may be so marked as to
suggest a diagnosis of scleroderma,
but unlike scleroderma, the damage
is confined to sun-exposed areas.
ERYTHROPOIETIC PROTOPORPHYRIA
 The
skin disease of erythropoietic protoporphyria
takes a different form: an unusual
syndrome of immediate, severe photosensitivity,
felt by the patient as warmth, burning,
stinging and pain in sun-exposed
areas (Read Erythropoietic
protoporphyria). Typically patients
have a threshold: and beyond a set
period of exposure (usually 30 minutes),
will learn to expect the symptoms
to begin. When seen immediately
after sun exposure, the skin may
be erythematous and oedematous.
Unlike the other porphyrias, the
patients do not develop erosions
and blisters, but rather an unusual
but characteristic pattern of thickening
and coarsening of the skin over
the bridge of the nose and the knuckles.
RELATIONSHIP BETWEEN LIGHT EXPOSURE
AND THE ACUTE ATTACK
There is no such
relationship. Some patients mistakenly
believe that exposure to sunlight
will precipitate critical complications
such as the acute attack and paralysis.
This is totally erroneous. The worst
consequence of sun-exposure is aggravated
skin disease.
MANAGEMENT OF SKIN DISEASE
Read the following:
Management
of skin disease.
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