Lassus 1983.

Methods	Randomised, parallel‐arm trial Number of centres not stated Period of inclusion not stated
Participants	Inclusion criteria Severe palmoplantar pustulosis Remission after maximum 16 weeks of Tigason Exclusion criteria Not stated Baseline data: randomised to Tigason 0.14 to 0.38 mg/kg/d (n = 11) or placebo (n = 14) Mean age, male/female, duration of the condition: not stated for this particular group of participants Proportion with psoriatic lesions elsewhere: not specified Withdrawal: 4 participants (in the placebo group) were lost because of adverse events (marked hair loss) but not specified if they were included in the analysis
Interventions	Intervention A: oral Tigason 0.14 to 0.38 mg/kg/d (11 participants) Control intervention B: placebo (14 participants) Co‐interventions: none Duration of treatment: 6 months
Outcomes	No primary or secondary outcomes pre‐specified
Notes	Funding: not reported
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Patients were randomised to either Tigason or placebo for 6 months" Comment: insufficient information about the sequence generation process to permit judgement
Allocation concealment (selection bias)	Unclear risk	Comment: no information on method to guarantee allocation concealment
Blinding of participants and personnel (performance bias) All outcomes	High risk	Quote: "double‐blind placebo‐controlled" Comment: likely that blinding could have been broken because of Tigason's side effects, mainly symptoms from skin and/or nasobuccal mucous membranes
Blinding of outcome assessment (detection bias) All outcomes	High risk	Quote: "double‐blind placebo‐controlled" Comment: likely that blinding could have been broken because of etretinate's side effects, mainly symptoms from skin and/or nasobuccal mucous membranes
Incomplete outcome data (attrition bias) All outcomes	High risk	Quote: "In the placebo group, there were initially 14 patients but 4 of them were dropouts (side effects = marked hair loss)" Comment: all dropouts were in the placebo group, and not clearly mentioned if they were included in the analysis
Selective reporting (reporting bias)	Unclear risk	Comment: no protocol found to guarantee that all planned outcomes are presented in the results