June 2006
Diagnosis: Solar urticaria
Histopathology : Mixed perivascular and interstitial acute
and chronic inflammatory infiltrate; consistent with urticaria.
Patient course:
The patient was placed on antihistamines and light treatment
for hardening was discussed as possible further treatment.
Discussion:
Solar urticaria is a rare photodermatosis characterized by
pruritus, stinging, erythema, and wheal formation shortly after
irradiation, comprising approximately 4-5% of photosensitive dermatoses
worldwide, without racial predilection. These symptoms usually
remit within minutes to hours without any residual signs or symptoms,
almost as rapidly as they began. However, there can be a latency
period of several hours between exposure and whealing. In this
way, solar urticaria is analogous to the other urticarias (1).
Because of the acuity and severity of symptoms, and the absence
of a known mechanism or treatment, this disorder can be quite
disabling and difficult to manage. It is hypothesized
that solar urticaria is caused by type I hypersensitivity reaction.
Neoantigens are postulated to be formed secondary to photoactivation
which then take part in an immediate-type antigen-antibody interaction.
Two types of immune reaction have been proposed: a type I response
in which immunoglobulin E (IgE)-mediated hypersensitivity is to
unique photoallergens generated only in solar urticaria patients,
versus a type II response in which photoallergens are found in
the general population but are uniquely antigenic in solar urticaria
patients. This classification is based on the fact that intradermal
injection of serum from a solar urticaria patient has been shown
in some, but not all cases, to transfer the condition to a healthy
individual (2). Photoactivation has been shown from a wide action
spectrum (290-800nm) further supporting a heterogenous mechanism
for photoallergen formation, perhaps related to the size and configuration
of these reactive precursors. In addition, investigators have
demonstrated inhibition spectra, in addition to augmentation spectra,
that take part in this process. These are usually longer wavelengths
that are thought to destroy or revert photoallergens into non-immunogenic
compounds. Then end result of these antigen-antibody reactions
is mast cell degranulation leading to histamine release.
When making this diagnosis, it is crucial to distinguish solar
urticaria from other photoeruptions including polymorphous light
eruption (PMLE), erythrogenic protoporphyria, various forms of
lupus, photoallergic reactions and phototoxic reactions. In general
PMLE is much more common than solar urticaria, usually displays
a hardening phenotype versus the heightening of symptoms from
decreased stimulation seen in solar urticaria, and the lesions
are usually not as transient as those in solar urticaria after
cessation of stimuli. Erythrogenic protoporphyria usually manifests
earlier in life. Lupus erythematous usually has a classic appearance
with supporting laboratory work. Photoallergic and toxic reactions
usually have cutaneous patterns reminiscent of the inciting stimuli
and often have residual signs and symptoms compared to solar urticaria.
Phototesting, as in this case, may be performed to determine the
action spectra responsible for symptoms. Additionally, laboratory
workup including plasma porphyrin levels, followed by quantitative
urine and fecal porphyrin collections if indicated, and serologic
tests to rule out connective-tissue disease such as antinuclear
antibody (ANA), Ro and La antibodies may be performed.
Consistent with the proposed mechanism of solar urticaria, treatment
consists of avoidance of the identified reactive wavelengths,
antihistamines and tolerance induction via graded challenges to
incremental amounts of light for which PUVA has been documented
to have a more sustained response than UVB, although all forms
of hardening are thought to be fairly short lived. Other forms
of immune modulation such as antimalarials and plasma exchange
have also been reported with limited efficacy (3).
Histologic changes are typically found in the dermis in the
form of vasodilatation, increased permeability of the vascular
endothelium, and edema. Eosinophil infiltration and deposition
of eosinophil granule proteins in the dermis are prominent during
early stages of the lesion. Neutrophils are found in increased
numbers around the upper dermal vessels. Dermal mast cells may
increase in number. After 24 hours, the dermal infiltrate is predominantly
composed of mononuclear leukocytes.
Solar urticaria is usually a chronic condition, with few patients
experiencing spontaneous remission, as illustrated in the cohort
of 87 patients followed by Beattie et. al (4). In this study,
the majority of the cohort followed was affected after 10 years.
Therefore, patient education is essential in this persistent and
chronic disease with is otherwise a benign disorder not affecting
systemic health.
References:
1. Monfrecola G, Nappa P, Pini D. Solar urticaria with delayed
onset: a case report. Photodermatology 1988: 5: 103-4.
2. Honigsmann H. Mechanisms of phototherapy and photochemotherapy
for photodermatoses. Dermatologic Therapy 2003: 16: 23-27.
3. Roelandts R. Diagnosis and treatment of solar urticaria. Dermatologic
Therapy 2003: 16: 52-56.
4. Beattie PE, Dawe RS, Ibbotgson SH, Ferguson J. Characteristics
and prognosis of idiopathic solar urticaria. Archives Dermatology
2003: 139: 1149-1154.
This case was presented by Drs. Daniel Popkin, Beatriz Tapia,
Anne Lind and Caroline Mann.
