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| Actinic Prurigo |
Actinic
Prurigo
Actinic prurigo, also known
as prurigo or hydroa aestivale or Hutchinson summer, is a photodermatosis that
is characterized by intensely pruritic papulonodular lesions, primarily but not
exclusively affecting sun-exposed areas. The condition is usually seen in
prepubescent females and typically in the spring and can persist through
winter. In severe cases, excoriations, cheilitis, conjunctival disease, and
scarring may develop. The disease has a strong genetic component and is
commonly seen in American Indians of North, Central, and South America. This
activity reviews the evaluation and management of actinic prurigo and
highlights the interprofessional team's role in caring for patients with this
condition.
Introduction
Actinic prurigo (AP) is a
rare form of idiopathic photodermatosis that primarily affects sun-exposed
areas of the skin. The affected regions of the skin typically
include the face, neck, and dorsal surface of the upper extremities.
Sun-protected areas of the skin, such as the buttocks, have also been
described. Actinic prurigo typically manifests in the spring as symmetric
intensely pruritic papulonodular dermatitis and can persist into the winter
months. In severe cases, excoriations, cheilitis, conjunctival disease, and
scarring may develop. Actinic prurigo is typically described in
prepubescent females but can occur at any age or gender. The disease
has a strong genetic component and is more commonly seen in American Indians of
North, Central, and South America. The diagnosis is mainly clinical. Disease
management begins with sun protection and sunlight avoidance. Treatment
involves topical antihistamines, corticosteroids, photochemotherapy (PUVA), as
well as systemic therapies for severe cases. Without treatment, this disease
course remains chronic and can persist into adulthood.
Etiology
The etiology remains
unclear, but there is a strong genetic component suggesting an autoimmune basis
for actinic prurigo. The human leukocyte antigen DR4 allele variant is present
in 90% of the cases, especially the DR4 subtype DRB1*0407, which is seen
in 60% of cases. Aside from a genetic predisposition,
environmental exposure, especially to ultra-violet light, seems to be a major
provoking factor. Older studies suggested an increased prevalence of actinic
prurigo in populations residing in high-altitude areas with an improvement in
the disease severity if the affected individual moved to lower altitudes.
Epidemiology
Actinic prurigo is a rare
photodermatosis in the United States. However, actinic prurigo is more common
in the American Indian populations of North, Central, and South America. The
disease can affect both genders but is more commonly described in female
patients. Actinic prurigo can manifest at any age, although the
disease typically presents in prepubescent individuals with the mean onset
before age 10. Some studies suggest an increased prevalence of actinic prurigo
in certain geographic areas with dry, warm climates at an altitude of at least
1000 meters above sea level.
Pathophysiology
The pathophysiology of
actinic prurigo remains largely unclear. Still, evidence suggests the
disease process is driven by a delayed type-IV hypersensitive response to
ultraviolet A and B (UVA and UVB) radiation in genetically predisposed
individuals. Both TH1 and TH2 lymphocytic processes have been
implicated in the disease process. Multiple studies note the presence
of eosinophils and mast cells in the dermal layers of involved
tissue, which suggests a type-IVb (TH2)-driven response specifically. TH2
lymphocytes secrete IL-4, IL-5, and IL-13, which promote IgE and IgG4
production by B cells. These immunoglobulins stimulate eosinophils and mast
cells. Individuals with moderate to severe actinic prurigo have been found to
have markedly elevated IgE levels, further supporting a type-IVb
(TH2) hypersensitive reaction.
Histopathology
Biopsy alone is not
sufficient to diagnose actinic prurigo, but histopathology can help aid
diagnosis and exclude other disease processes with similar presentations. Skin
biopsies will show hyperkeratosis, spongiosis, and acanthosis in the epidermis
with lymphocytic perivascular infiltration in the dermis. A lip biopsy will
show lymphoid germinal centers in the lamina propria, which can help
distinguish actinic prurigo from the polymorphous light eruption. Studies have
also described an infiltration of eosinophils and mast cells in the underlying
mucosa of affected lesions, which correlate with a delayed type-IVb hypersensitive
response.
History and Physical
Patients with actinic prurigo will typically present in early
spring as sunlight becomes more prevalent, and individuals spend more time
exposing their skin to sunlight. Patients will present with intensely itchy,
erythematous papulonodular lesions on predominantly sun-exposed areas of the
skin. The face, especially over the zygomatic arches, nasal bridge, lower lip,
and conjunctiva, is typically affected. However, lesions may develop
anywhere on the neck, trunk, extremities, and even non-sun exposed areas such
as the buttocks. Since the lesions are intensely pruritic, excoriations, skin
thickening, scarring, and hyper- or hypopigmentation may occur.
Actinic
cheilitis has been described as a hallmark finding in patients with
actinic prurigo. Individuals may present with actinic cheilitis as a
solitary finding or in concurrence with more widespread papulonodular
lesions.
Evaluation
Actinic prurigo is typically
diagnosed clinically with a detailed history and physical exam. Patients
will report the characteristic symptoms of severely pruritic papulonodular
erythematous skin lesions that began in the spring or summer months. Patients
may or may not report a direct correlation between exposure to sunlight and
disease onset. Diagnosis can be aided by skin photo-testing, histologic
evaluation, and genetic screening for the HLA DR4 allele variant. Clinicians
often perform laboratory testing and immunofluorescence studies to rule out
lupus erythematosus and other photosensitive dermatoses.
Treatment / Management
Minor cases of actinic prurigo can be treated with sun-avoidance
alone. Proper sun protection includes avoiding sunlight by staying indoors or
in shaded areas, wearing protective clothing, sunglasses, and wide-brim hats,
and using a broad-spectrum sunscreen. Topical corticosteroids and non-sedating
antihistamines will provide relief for acute episodes. The more severe and
persistent disease requires treatment with systemic therapies such as
antimalarials, tetracyclines, and systemic corticosteroids.
Thalidomide
has been described as the hallmark therapy for severe refractory cases of
actinic prurigo. Treatment with thalidomide has a major limiting side effect
profile, which includes peripheral neuropathy and teratogenicity. Treatment
with thalidomide is contraindicated during pregnancy or in individuals trying
to become pregnant. Females of childbearing age must use contraception during
therapy with thalidomide. Screening for peripheral neuropathy is typically
initiated pre-treatment and continued throughout the treatment process.
Alternative
immunosuppressive regimens with agents like cyclosporine A have
been described as successful as well.
Photochemotherapy with psoralen and ultraviolet A (PUVA) has also been
shown to successfully manage symptoms and treat skin changes caused by
actinic prurigo.
Differential Diagnosis
Originally, actinic prurigo was thought to be a hereditary
type of polymorphous light eruption (PMLE), more common idiopathic
photodermatoses. Genetic testing and the unique clinical presentation of
actinic prurigo now support two separate disease entities. The HLA-DR4 allele,
specifically the DRB1*0407 subtype, is strongly associated with actinic
prurigo and not PMLE. Actinic prurigo also has an earlier age of onset and
frequently presents with cheilitis and sometimes conjunctivitis, which is never
seen in patients with PMLE. When suspecting actinic prurigo, laboratory tests
are also necessary to rule out systemic diseases such as lupus erythematosus or
porphyria.
- Polymorphous light eruption
- Systemic lupus erythematosus
- Porphyria
Prognosis
Actinic prurigo is a chronic
disease process and can reoccur with repeated sun exposure. Treatment with
immunosuppressive agents like thalidomide and cyclosporine A has been shown to
be effective at long-term suppression of symptoms. Some adolescents may have
spontaneous resolution of symptoms and may not demonstrate disease
progression into adulthood.
Complications
Complications of actinic prurigo include:
- Secondary bacterial infections
- Contact dermatitis
- Impetigo
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