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Biomedical subjects

John L M Hawk

Publications and source records attributed to John L M Hawk.

7 recordsLinked to original sources
PubMed2006

Randomized double-blind trial of the treatment of chronic plaque psoriasis: efficacy of psoralen-UV-A therapy vs narrowband UV-B therapy.

OBJECTIVE: To compare the efficacy of oral psoralen-UV-A (PUVA) therapy with that of narrowband UV-B (NB-UVB) therapy in patients with chronic plaque psoriasis. DESIGN: Double-blind randomized study. SETTING: Phototherapy unit in a university hospital. Patients Ninety-three patients with chronic plaque psoriasis. Interventions Twice-weekly NB-UVB or PUVA therapy, starting at 70% of the minimum phototoxic or erythema dose, with 20% incremental increases. Patients were treated until clearance, up to a maximum of 30 sessions; those with clearance were followed up until relapse or for 12 months. MAIN OUTCOME MEASURES: Proportion of patients achieving clearance, number of treatments to clearance, and, among those with clearance, the proportion remaining in remission at 6 months. RESULTS: Patients with skin types V and VI had a lower rate of clearance than those with skin types I through IV (24% vs 75%; P = .001). In patients with skin types I through IV, PUVA was significantly more effective than NB-UVB at achieving clearance (84% vs 65%; P = .02). The median number of treatments to clearance was significantly lower in the PUVA group (17.0 vs 28.5; P<.001). More patients treated with PUVA vs NB-UVB were reported to have erythema at some stage during treatment (49% vs 22%; P = .004), although this difference may have been due to ascertainment bias. Six months after the cessation of therapy, 68% of PUVA-treated patients were still in remission vs 35% of NB-UVB-treated patients. Conclusion Compared with NB-UVB, PUVA achieves clearance in more patients with fewer treatment sessions and results in longer remissions.

Administration, Oral↗
PubMed2006

Photoadaptation during narrowband ultraviolet-B therapy is independent of skin type: a study of 352 patients.

Understanding how photoadaptation differs between individuals is important when considering susceptibility to the beneficial and harmful effects of sunlight exposure and when determining optimal phototherapy regimens. Most narrowband UVB (NB-UVB) regimens start with 70% of the minimal erythema dose (MED) with 20% increments at each treatment thereafter. We retrospectively studied 352 skin types I-IV psoriatic patients having twice weekly treatment with this regimen. Patients with high skin types tended to have high MEDs (P<0.001). By session 20 the proportion of patients who had developed erythema was approximately 60% regardless of MED. Among patients who developed erythema, the number of treatments before erythema occurred did not differ between skin types (P=0.33). We conclude that patients with high skin types photoadapt approximately equally per physical unit of UVR in comparison to those with low skin types, but they have greater photoadaptation in absolute terms because they are able to tolerate a higher initial dose of radiation. Differences in skin type or MED are not associated with clinically important differences in tendency to erythema during a standard 70/20% NB-UVB twice-weekly regimen. This regimen is suitable for all skin types I-IV patients regardless of skin type or MED.

Adaptation, Physiological↗
PubMed2005

The effect of solar-simulated radiation on the elicitation phase of contact hypersensitivity does not differ between controls and patients with polymorphic light eruption.

It has been suggested that polymorphic light eruption (PLE) is characterized by a failure of ultraviolet radiation (UVR)-induced immunosuppression, resulting in a type-IV hypersensitivity response to photoinduced antigens. We measured the effect of solar-simulated radiation (SSR) on the elicitation phase of contact hypersensitivity to 2,4-dinitrochlorobenzene (DNCB), in ten PLE patients and 11 controls. Subjects were given a sensitizing dose of DNCB, and 3 wk later were exposed to 0.75 and 2 minimum erythema doses (MED) of SSR on the upper inner arm. Immediately and 24 h later these sites, and a non-irradiated control site, were challenged with DNCB. The resulting increase in skin thickness was measured with high-frequency ultrasound. Overall, 2 MED caused 17%-20% suppression of elicitation responses (compared with 93% suppression of sensitization reported previously), but the effect of SSR varied greatly between subjects, with some subjects showing potentiated responses, which may be of relevance to false-positive reactions in photopatch testing. In a repeated measures general linear model, SSR overall caused significant suppression of responses (p<0.001); there was less suppression in older subjects (p=0.009) but there was no significant difference between PLE patients and age-matched normal controls. These results contrast with our previous finding of a resistance to UVR-induced suppression of sensitization to DNCB in PLE. This difference may reflect the greater importance of Langerhans cells in the sensitization phase, and is consistent with the hypothesis that PLE arises from impaired suppression of Langerhans cell activation or migration.

Adult↗
PubMed2004

Ultraviolet-radiation-induced erythema and suppression of contact hypersensitivity responses in patients with polymorphic light eruption.

Ultraviolet-radiation suppresses cell-mediated immunity in healthy humans. It has been postulated that, in the short term, this immunosuppression prevents autoimmune responses to ultraviolet-radiation damaged skin. Patients with polymorphic light eruption (PLE) demonstrate abnormal responses to ultraviolet-radiation suggestive of an immune response to an ultraviolet-radiation-induced antigen. We investigated whether PLE patients (n=22) were resistant to ultraviolet-radiation-induced immunosuppression compared to skin-type, aged-matched controls (n=23). Groups of patients and controls (six subjects per group) received a single dose of solar-simulated ultraviolet-radiation of either 0, 0.6, 1 or 2 minimal erythema doses (MED). Erythema was quantified using a reflectance meter and all volunteers were sensitised on the irradiated site with dinitrochlorobenzene. Contact hypersensitivity responses (CHS) to dinitrochlorobenzene were quantified after challenge using ultrasound. Ultraviolet-radiation-induced erythema was comparable in patients and controls. CHS was comparable in unirradiated patients and controls. UVR-induced a dose-dependent suppression of CHS in all volunteers but patients were more resistant to immunosuppression after 1MED. Exposure to 1MED suppressed CHS by 78% in controls but induced less suppression in patients (44%, p < 0.01). Our data suggest that PLE patients have a flaw in their immunoregulatory response to ultraviolet-radiation it is only apparent over a narrow dose range around 1 MED.

Adult↗
PubMed2002

Photosensitivity disorders: cause, effect and management.

Abnormal photosensitivity syndromes form a significant and common group of skin diseases. They include primary (idiopathic) photodermatoses such as polymorphic light eruption (PLE), chronic actinic dermatitis (CAD), actinic prurigo, hydroa vacciniforme and solar urticaria, in addition to drug- and chemical-induced photosensitivity and photo-exacerbated dermatoses. They can be extremely disabling and difficult to diagnose. PLE, characterized by a recurrent pruritic papulo-vesicular eruption of affected skin within hours of sun exposure, is best managed by restriction of ultraviolet radiation (UVR) exposure and the use of high sun protection factor (SPF) sunscreens. If these measures are insufficient, prophylactic phototherapy with PUVA, broadband UVB or narrowband UVB (TL-01) for several weeks during spring may be necessary. CAD manifests as a dermatitis of chronically sun-exposed skin. Again, UVR exposure needs to be restricted; cyclosporine, azathioprine or PUVA may also be necessary. Actinic prurigo is characterized by the presence of excoriated papules and nodules on the face and limbs, most prominent and numerous distally. Actinic prurigo is managed again by restriction of UVR and the use of high SPF sunscreens; PUVA or broadband UVB therapy, or low doses of thalidomide may be necessary. Hydroa vacciniforme causes crops of discrete erythematous macules, 2 to 3mm in size, that evolve into blisters within a couple of days of sun exposure. Treatment for this rare disease is difficult; absorbent sunscreens and restricted UVR exposure may help. Solar urticaria is characterized by acute erythema and urticarial wealing after exposure to UVR. Treatment options for solar urticaria include non-sedating antihistamines such as fexofenadine and cetirizine; other options include absorbent sunscreens, restriction of UVR at the relevant wavelength, maintenance of a non-responsive state with natural or artificial light exposure and plasmapheresis. Industrial, cosmetic and therapeutic agents can induce exogenous drug- or chemical-induced photosensitivity. The clinical pattern is highly varied, depending on the agent; treatment is based on removal of the photosensitizer along with restriction of UVR exposure. Predominantly non-photosensitive dermatoses may also be exacerbated or precipitated by UVR; exposure to UVR should be reduced and sunscreens should be advocated, along with appropriate treatment of the underlying disease.

Acute Disease↗