Hydroa vacciniforme (HV) is a rare, chronic photosensitivity disorder which chiefly occurs in children. The disease is characterised by the eruption of inflamed bumps and fluid-filled blisters (vesicles) on the skin following exposure to sunlight. Commonly presenting on the face, ears and hands, these vesicles heal over time as pox-like or “vacciniform” scars. Ultraviolet A (UVA) radiation (320-400nm) is the main wavelength of light which has been demonstrated to induce symptoms.
HV was first described in 1862 in France by Antoine Pierre Ernest Bazin and Emile Baudot. The vast majority of cases begin in childhood and resolve spontaneously in adolescence or early adulthood. The disease is not fatal, however, due to its prevalence in pediatric patients, the level of discomfort suffered and the long-term scarring which results, HV is considered to have a high impact upon patient quality of life.
HV is a rare disease and prevalence data is limited, but in Scotland rates are reported as approximately one in 300,000. Occurring predominantly in children aged 3-15, one study indicates a median onset age of 7.9 years for HV. A few cases have also been reported in infants and elderly people up to 60 years of age. There is a higher incidence of HV in females and the disease also presents at a younger age in female patients than in males. It has been found, however, that there is a longer course of the disease in males.
The exact cause of HV is unknown, though the distribution of the lesions on sun exposed areas of skin tend to suggest a causal relationship with sunlight. Reproduction of HV papules following repeated exposure to artificial sources of UV light indicates that UVA is the wavelength responsible for the symptoms. While the precise pathologic mechanism is unknown, HV is believed to be caused by an auto-immune disorder. Hence, it is classified along with polymorphic light eruption, actinic prurigo, chronic actinic dermatitis and solar urticaria as an IMP or “immunologically mediated photodermatosis”. These are a group of immune-influenced diseases which elicit symptoms in the skin upon exposure to light, mainly that in the UVA spectrum.
There have been two familial cases of HV in siblings which have led to the notion of there being a genetic component to the disease, though further study is required to substantiate this theory. In addition, a single case has been reported following treatment with the immunosuppressant drug “cyclosporine”. Due to the inconsistent responses to a broad range of treatments and disparity in the ages of onset/remission, some also speculate that HV may be a disease arising from different origins that present as a similar clinical syndrome.
The first symptoms of HV generally appear on the cheeks and nose in the spring or summer months, though can occur on any sun-exposed skin. Initially patients will experience a mild burning or tingling sensation, this has also been described as stinging and itching. Erythema (redness of skin caused by inflammation) leads to the development of multiple small blisters, bumps or lesions within 30 minutes to 2 hours following sun exposure. These lesions are originally taut and swollen with accumulated fluid then slowly form necrotic, pox-like crusts and scabs (sometimes blackish in colour). They heal over several days, eventually becoming light or unpigmented scars which tend to be depressed or indented; these may last for a number of years. The vesicles, or blisters, recur upon subsequent exposure to solar radiation.
Some HV patients experience ocular problems – light sensitivity (photophobia), mild inflammation of the eyes (keratoconjunctivitis) and clouding/inflammation of the cornea (the front part of the eye), known as keratitis. Uncommon symptoms, described by only a couple of patients, include: bone and cartilage reabsorption, earlobe mutilation, separation of nails from their nail-beds and systemic (whole-body) effects.
A high rate of Epstein-Barr Virus (EBV) infection in HV patients has been reported in medical literature. The pathological association between the disease and the virus is unclear, though one theory is that the disease is mediated by the T-cells of the immune system which can become infected with EBV. One study revealed that individuals with severe HV had more chronic, active infections, whereas those with more subtle forms of the disease tended to have mild or latent infections.
Severe forms of HV-like eruptions have been linked with an aggressive type of T-cell lymphoma (EBV-associated) mainly found in children from Asia and Latin America. While some researchers claim that HV can evolve into T-cell lymphoma, most insist that this is a disease distinct from the classical HV.
Diagnosis and Treatment
HV diagnosis is difficult since the characteristic lesions are similar to those produced by other skin disorders such as porphyria and polymorphous light eruption. Repetitive UVA phototesting involves deliberately exposing a section of skin to an artificial source of UVA radiation to determine the cutaneous reaction generated. This is the best available method of diagnosis, though it is by no means definitive.
A range of preventative treatments have been employed with efficacy varying between patients. To date, no consistent therapy has been discovered. The mainstay of treatment remains photoprotection of skin; with UVA blocking sunscreens, tight-weave, sun-protective clothing (including wide brimmed hats) and avoidance of sunlight. When lesions occur they are usually treated with wet dressings and topical antibiotics.
The following treatments have been trialed with varying success:
Narrowband and broadband UVB phototherapy – The aim of UVB phototherapy is to harden the skin of HV patients against the lesion-inducing effects of UVA radiation without provoking symptoms. UVB radiation consists of wavelengths between 280 and 315 nanometres (nm), Traditional sources of UVB radiation give off wavelengths of light across the spectrum (broadband). It has been found that the shorter wavelengths are particular harmful and more carcinogenic than longer wavelengths. Moreover, it is the longer wavelengths which generally provide greater therapeutic effects for a range of skin disorders (commonly psoriasis). Thus, narrowband therapy was developed to utilize only those wavelengths which provided beneficial effects. Special tubes have been created which emit the wavelengths necessary to produce the therapeutic effect (305-315); for instance, the phosphor tube light (TL-01) emission is 311 to 312 nm. Narrowband is preferable to broadband therapy as it has remedial value while minimising potential damage. UVB phototherapy has been shown to reduce the severity of HV in several cases, but some consider it too dangerous due to the known deleterious effects of UV radiation. Furthermore, the treatments, which are administered several times over weeks or months, often involve the patient standing or lying in a booth with tube lights for a period of time; some children may find this experience intimidating.
Fish oil/Omega 3 oral supplements – A diet rich in omega-3 fatty acids (commonly obtained from fish oil) has traditionally been shown to reduce erythema in response to UV radiation in a range of patients, particularly those with polymorphic light eruption. It was therefore hoped to reduce the sensitivity of skin of patients with HV. One study of 3 boys resulted in significant improvement in one patient, moderate improvement in the second and no noticeable reduction in the third’s lesions at all. This is typical of the unpredictable and variable nature of HV treatments to date.
Pharmaceutical therapies – A few individuals treated with oral antimalarials such as chloroquine noted fewer, less severe lesions and increased resistance to UVA radiation, but overall these have been found widely insufficient. Some patients have been shown to benefit from carotenoids such as beta-carotene (an antioxidant) and canthaxanthin, with a few even claiming total resolution of symptoms. Immunosuppressant drugs, including cyclosporine A and azathioprine, can be given alone or intermittently with steroids, this option has also had some success.
Most cases of HV will remit by late adolescence or early adulthood, but a few have been reported to continue into adulthood. Lifelong HV symptoms have been encountered but are extremely rare. There has been the occasional report of late onset HV in the patients 20’s, with one as late as 58 years of age. As previously mentioned, boys tend to suffer longer than girls and the average duration of the disease from follow-up studies has been established as nine years.
Hydroa Vacciniforme online support group, for those with a family member suffering from the condition.
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