Lawrence 1984.

Methods	Randomised, parallel‐arm trial One centre in the UK Period of inclusion not stated
Participants	Inclusion criteria Clinically diagnosed with palmoplantar pustular psoriasis or hyperkeratotic psoriasis of palms and soles that might be associated with psoriatic lesions elsewhere Age ≥ 18 years Exclusion criteria Pregnancy Kidney insufficiency Liver insufficiency Baseline data: randomised to PUVA therapy‐etretinate (1 mg/kg) (n = 10) or PUVA therapy‐placebo (n = 10) Mean age, years: 60.6 ± 3; 52.2 ± 4.6 Male/female: 3/7; 1/9 Duration of the disease, years: 16 ± 4.8; 9.3 ± 3.2 Proportion of participants with psoriatic lesions elsewhere: 9/17 Withdrawal: 1 dropout in the PUVA therapy‐placebo group (diverticulitis)
Interventions	Intervention 1 A: etretinate (1 mg/kg/d) (10 participants) Intervention 2 B: placebo (10 participants) Co‐interventions: oral PUVA therapy Duration of treatment: 20 weeks (2 weeks of etretinate or placebo alone and 18 weeks maximum of PUVA therapy‐etretinate or PUVA therapy‐placebo)
Outcomes	No primary or secondary outcome pre‐specified Clearance (defined as disappearance of all pustules with mild or absent scaling and erythema) according to the extent of scaling and erythema scored as severe, moderate, mild, none (3‐0) and the number of new pustules Cumulative UVA dose Number of treatments Duration of therapy
Notes	Roche Products Ltd supported the study and provided the etretinate. Dr Parker was supported by the Newcastle Health Authority Research Committee
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Quote: "Patients were randomly allocated to either PUVA plus placebo (PUVA‐placebo) or PUVA plus etretinate (PUVA‐etretinate)" 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: "The trial was conducted as if double‐blind, although in most patients differences in side‐effects and patient response made a double‐blind assessment impossible" Comment: blinding probably broken
Blinding of outcome assessment (detection bias) All outcomes	High risk	Quote: "The trial was conducted as if double‐blind, although in most patients differences in side‐effects and patient response made a double‐blind assessment impossible" Comment: blinding probably broken
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Quote: "Nineteen patients completed the study. One patient, who was receiving placebo, was withdrawn during the sixth week of the study because she developed acute diverticulitis, presumably unrelated to treatment" Comment: 1 participant dropped out because of diverticulitis, but not mentioned whether she was 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