House dust mite reduction and avoidance measures for treating eczema Edited (no change to conclusions)

Abstract

Background

Eczema is an inflammatory skin disease that tends to involve skin creases, such as the folds of the elbows or knees; it is an intensely itchy skin condition, which can relapse and remit over time. As many as a third of people with eczema who have a positive test for allergy to house dust mite have reported worsening of eczema or respiratory symptoms when exposed to dust.

Objectives

To assess the effects of all house dust mite reduction and avoidance measures for the treatment of eczema.

Search methods

We searched the following databases up to 14 August 2014: the Cochrane Skin Group Specialised Register, CENTRAL in The Cochrane Library (2014, Issue 8), MEDLINE (from 1946), Embase (from 1974), LILACS (from 1982), and the GREAT database. We also searched five trials registers and checked the reference lists of included and excluded studies for further references to relevant studies. We handsearched abstracts from international eczema and allergy meetings.

Selection criteria

Randomised controlled trials (RCTs) of any of the house dust mite reduction and avoidance measures for the treatment of eczema, which included participants of any age diagnosed by a clinician with eczema as defined by the World Allergy Organization. We included all non‐pharmacological and pharmacological interventions that sought to reduce or avoid exposure to house dust mite and their allergenic faeces. The comparators were any active treatment, no treatment, placebo, or standard care only.

Data collection and analysis

Two authors independently checked the titles and abstracts identified, and there were no disagreements. We contacted authors of included studies for additional information. We assessed the risk of bias using Cochrane methodology.

Main results

We included seven studies of 324 adults and children with eczema. Overall, the included studies had a high risk of bias. Four of the seven trials tested interventions with multiple components, and three tested a single intervention. Two of the seven trials included only children, four included children and adults, and one included only adults. Interventions to reduce or avoid exposure to house dust mite included covers for mattresses and bedding, increased or high‐quality vacuuming of carpets and mattresses, and sprays that kill house dust mites.

Four studies assessed our first primary outcome of 'Clinician‐assessed eczema severity using a named scale'. Of these, one study (n = 20) did not show any significant short‐term benefit from allergen impermeable polyurethane mattress encasings and acaricide spray versus allergen permeable cotton mattress encasings and placebo acaricide spray. One study (n = 60) found a modest statistically significant benefit in the Six Area, Six Sign Atopic Dermatitis (SASSAD) scale over six months (mean difference of 4.2 (95% confidence interval 1.7 to 6.7), P = 0.008) in favour of a mite impermeable bedding system combined with benzyltannate spray and high‐filtration vacuuming versus mite permeable cotton encasings, water with a trace of alcohol spray, and a low‐filtration vacuum cleaner. The third study (n = 41) did not compare the change in severity of eczema between the two treatment groups. The fourth study (n = 86) reported no evidence of a difference between the treatment groups.

With regard to the secondary outcomes 'Participant‐ or caregiver‐assessed global eczema severity score' and the 'Amount and frequency of topical treatment required', one study (n = 20) assessed these outcomes with similar results being reported for these outcomes in both groups. Four studies (n = 159) assessed 'Sensitivity to house dust mite allergen using a marker'; there was no clear evidence of a difference in sensitivity levels reported between treatments in any of the four trials.

None of the seven included studies assessed our second primary outcome 'Participant‐ or caregiver‐assessed eczema‐related quality of life using a named instrument' or the secondary outcome of 'Adverse effects'.

We were unable to combine any of our results because of variability in the interventions and paucity of data.

Authors' conclusions

We were unable to determine clear implications to inform clinical practice from the very low‐quality evidence currently available. The modest treatment responses reported were in people with atopic eczema, specifically with sensitivity to one or more aeroallergens. Thus, their use in the eczema population as a whole is unknown. High‐quality long‐term trials of single, easy‐to‐administer house dust mite reduction or avoidance measures are worth pursuing.

Author(s)

Helen Nankervis, Emma V Pynn, Robert J Boyle, Lesley Rushton, Hywel C Williams, Deanne M Hewson, Thomas Platts‐Mills

Abstract

Plain language summary

House dust mite reduction and avoidance measures for treating eczema 

Background 

Eczema is an intensely itchy skin disease that tends to involve skin creases, such as the folds of the elbows or knees. It is a worldwide problem affecting 5% to 20% of children. Around 2% of adults have the condition, and many have a more chronic and severe form. As many as a third of people with eczema who have a positive test for allergy to house dust mite have reported worsening of eczema or respiratory symptoms when exposed to dust. Ways to reduce or avoid exposure to house dust mite, such as covers for mattresses and bedding, increased or high‐quality vacuuming of carpets and mattresses, or sprays that kill the mites, could lessen the severity of eczema for those who are sensitive to house dust mite. In this review, we aimed to assess the effects of all house dust mite reduction and avoidance measures for the treatment of eczema.

Review question 

Do house dust reduction and avoidance measures provide a successful way to treat eczema?

Study characteristics 

We found seven randomised controlled trials, which included 324 adults and children with eczema. We conducted the search up to 14 August 2014. Two of the seven trials included only children; four included children and adults; and one only included adults. Four of the seven trials compared treatments made up of multiple different house dust mite reduction and avoidance measures, and three trials tested a single treatment. The treatments were compared against other house dust mite reduction or avoidance treatments, no treatment, a placebo intervention (e.g., cotton bed covers), or standard care only.

Key results 

We did not find any evidence to inform clinical practice. Some small treatment responses reported were in people with atopic eczema who were sensitive to one or more airborne allergens. We found no evidence of benefit in the other six included studies. Therefore, their use in the eczema population as a whole is unknown. High‐quality longer trials of single, easy‐to‐use house dust mite reduction or avoidance measures should be performed.

Quality of the evidence 

These seven very low‐quality (Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach) small trials do not provide enough evidence to recommend any of the house dust mite reduction and avoidance measures tested.

Author(s)

Helen Nankervis, Emma V Pynn, Robert J Boyle, Lesley Rushton, Hywel C Williams, Deanne M Hewson, Thomas Platts‐Mills

Reviewer's Conclusions

Authors' conclusions 

Implications for practice 

There can be little confidence in the observed beneficial effect on severity of eczema (measured using SASSAD) in one small, very low‐quality (GRADE approach) trial. As this treatment response has only been seen in those with atopic eczema, with specific sensitivity to one or more aeroallergens, its use in the eczema population as a whole is unknown. This trial also reported a high reduction in the level of mites in the treatment group, which agrees with suggestions from trials in allergic rhinitis (Nurmatov 2012): that it is only a very significant eradication of house dust mites that produces a clinically significant effect for eczema. The potential benefit from a small magnitude of effect needs to be weighed against the impact of sustaining the intervention regimen over long periods of time.

As none of the trials included in this review measured participant‐ or physician‐assessed eczema‐related quality of life, there is currently no evidence about the impact of house dust mite reduction and avoidance measures on people with eczema.

As many as a third of people with eczema who have a positive test for allergy to house dust mite have reported worsening of eczema or respiratory symptoms when exposed to dust. Four trials, three of which had atopic participants and a fourth that did not require sensitivity to allergens as an inclusion criterion, did not find any evidence of a reduction in the specific sensitivity to house dust mites over one year. This evidence hints that a 'home only' approach to dust mite eradication or reduction is ineffective with regard to the reduction of sensitivity to house dust mite in the eczema population. It is also not clear whether this reduction in a positive reaction to a skin prick test is a poor predictor of a clinically relevant allergy to house dust mite.

Many of the included trials used multiple different interventions simultaneously; however, the separate tasks themselves were not particularly onerous. It is plausible that families would be willing to use these interventions to see improvements in eczema. Where the interventions are particularly complex or intensive for parents and carers, there is potential for difficulties, such as lack of compliance and pressure on time, finances, and emotional energy.

The evidence available for house dust mite reduction and avoidance measures falls far short of a basis for influencing clinical practice.

Implications for research 

No significant clinical benefit of any house dust mite reduction or avoidance interventions lasting long enough to be satisfactory to those with a long‐term chronic condition such as eczema has yet been shown. The included studies have so far lacked methodological clarity, which leads to a lack of certainty about the modest positive results shown. Any future trials on reduction of house dust mite need to address the impact on eczema‐related quality of life. Future trials on reduction or avoidance of house dust mite for treating eczema are worth pursuing. Such trials should test a clearly reported single intervention against an appropriate comparator, such as a standard care package, only in order to be clear about which of the many candidate interventions are worth testing further. The eczema trial populations should be well characterised, and trials should provide at least a year of treatment with additional long‐term follow up.

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