Abstract: This review included only one trial (21 participants), which compared fish oil-derived (n-3) fatty acid-based lipid emulsion (50 mL per infusion (1.05 g eicosapentaenoic and 10.5 g docosahexaenoic acid)) (10 participants) to soya oil-derived (n-6) fatty acid-based lipid emulsion (50 mL per infusion (1.05 g eicosapentaenoic and 10.5 g docosahexaenoic acid)) (11 participants) administered intravenously twice daily for 10 days, with a total follow-up of 40 days. The study was conducted in a single centre in Germany in 18 men and three women, aged between 21 and 65 years, who were in hospital with acute guttate psoriasis and had mean total body surface involvement of 25.7% ± 20.4% (range 10 to 90). The study was funded by a company that produces the oil emulsions. We found no other evidence regarding non-antistreptococcal interventions used in clinical practice for guttate psoriasis, such as topical treatments (corticosteroids, vitamin D₃ analogues), systemic drugs, biological therapy, and phototherapy. The primary outcomes of the review were not measured, and only one of our secondary outcomes was measured: improvement in participant satisfaction measures and quality of life assessment measures. However, the study authors did report that there was rare skin irritation at the site of peripheral intravenous route, but the number of affected participants was not provided. Improvement between baseline and day 10, using a non-validated score assessed by participants themselves daily based on five items (appearance of lesions, impairment of daily life, pruritus, burning, and pain), was greater in the group that received the fish oil-derived (n-3) fatty acid-based lipid emulsion (75%) than in the group receiving the soya oil-derived (n-6) fatty acid-based lipid emulsion (18%) (one trial, 21 participants). However, these results are uncertain as they are based on very low-quality evidence. There is no evidence regarding topical and systemic drugs, biotherapy, or phototherapy in guttate psoriasis (we did not consider drugs that aimed to eradicate streptococcal infection because these are assessed in another Cochrane Review). We are uncertain of the effect of intravenously administered lipid emulsion on guttate psoriasis because the quality of the evidence is very low, due to risk of bias (unclear risk of bias for all domains), indirectness (the trial only included adults, and the follow-up from baseline was only 10 days), and imprecision (small number of participants). This review highlights the need for trials assessing the efficacy and safety of phototherapy and topical and systemic drugs for guttate psoriasis. There is also a need for studies that clearly distinguish the specific population with guttate psoriasis from the larger group of people with chronic plaque psoriasis, and children and young adults should be assessed as a distinct group.

Plain-language summary: We found one relevant study that compared the effects of giving injections into the vein of two different lipid (fat) emulsions twice daily for 10 days: one emulsion (two or more liquids that are often unmixable) was derived from fish oil, and the other was derived from soya oil. Participants were followed for a total of 40 days. The study was conducted in Germany in 21 adults (18 men and 3 women) aged 21 to 65 years, with a mean of involved skin surface of 25%, who were in hospital with acute guttate psoriasis. The study was funded by the company that produces the oil emulsions. Treatments for which we found no evidence include phototherapy and topical, oral, and biological medicines. The only study identified did not measure our two primary outcomes: percentage of people treated whose skin became clear (or almost clear) of lesions; and the side effects, or harms, of the treatments. Most of our secondary outcomes were also not measured, including worsening of guttate psoriasis or recurrence within a period of six months after the treatment has finished; and percentage of participants achieving a Psoriasis Area Severity Index 75 or Physician's Global Assessment of 1 or 2. The included study did not report measuring any harms of the treatments; however, the study authors did report rare skin irritation at site of injection, but did not provide the number of affected participants. The study participants rated some outcomes themselves, including the appearance of the skin lesions, the effects on their daily life, itching, burning, and pain. After 10 days of treatment, study participants who received the fish oil-derived lipid emulsion (75% of people in this group) rated greater improvements than those receiving the soya oil-derived lipid emulsion (18% of people in this group). However, these results are uncertain as they are based on very low-quality evidence. The evidence is current to June 2018. We rated the quality of the available evidence as very low. We considered that the study may be at risk of bias due to limitations in its design, and only a small number of people were included in the study. In addition, the study only enrolled adults, although guttate psoriasis is more common in children.