Lindelof 1989.

Methods	This was a randomised, double‐blind, internally‐controlled study. There was cross‐over to active treatment for the placebo‐treated group after 10 weeks. It was unclear if intention‐to‐treat analysis was conducted.
Participants	Inclusion criteria of the trial 24 participants with psoriasis of the nails of both hands; age range = 29 to 75 years. The psoriatic nails had various degrees of severity, ranging from nails of normal thickness with pits to very thickened hyperkeratotic nails.
Interventions	Each participant received 5 Gy of grenz rays given on 10 occasions at intervals of 1 week. The psoriatic nail of 1 hand received active treatment; the other hand was treated with placebo (the apparatus hummed without irradiation). The grenz ray machine factors were 10 kV, 10 mA, half‐value layer 0.02 mm Al, half‐value depth in tissue 0.5 mm, focus skin distance 10 cm. Active treatment was given to the former placebo‐treated hands after 10 weeks. The participants were then followed for 6 months.
Outcomes	Outcomes of the trial Clinical evaluation was done before the grenz ray therapy and after the 10th treatment. Photographs of the involved nails of both hands were obtained prior to the grenz ray treatment. The nails were examined for signs of psoriasis, i.e. pitting, onycholysis, oil drops, subungual hyperkeratosis, onychorrhexis, and psoriatic involvement of the proximal nail fold. After 10 weeks, the improvement of each of the psoriatic nail signs was judged, and an overall improvement was scored for each hand. The nails were scored as follows: almost complete recovery, moderate improvement, slight improvement, and no improvement. No carry‐over effect was present at cross‐over from placebo to active treatment.
Notes	The participant had been untreated for at least 6 months before the start of the study. 5 participants showed slight pigmentation of the grenz ray treated nail fold. No other local or systematic adverse reactions were noted.
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	Quote: '...double blind trial, participants were randomly allocated." Comment: This was probably done.
Allocation concealment (selection bias)	Unclear risk	Comment: No information about randomisation of the hands was available.
Blinding (performance bias and detection bias) Clinician/ Investigator	Low risk	Quote: "...double blind trial, neither the participant nor the evaluating doctor knew which side had received active grenz ray therapy."
Blinding (performance bias and detection bias) Participants	Low risk	Quote: "...double blind study, neither the participant nor the evaluating doctor knew which side had received active grenz ray therapy." Comment: Placebo was administered by allowing the apparatus to hum without irradiation.
Blinding (performance bias and detection bias) Outcome assessor	Low risk	Quote: "...double blind study, neither the participant nor the evaluating doctor knew which side had received active grenz ray therapy." Comment: The blinded doctor was the outcome assessor.
Incomplete outcome data (attrition bias) All outcomes	Low risk	2 participants failed to participate throughout the study, because of illness in their families
Selective reporting (reporting bias)	High risk	The nail signs were not separately discussed in the results.
Other bias	Unclear risk	There was no information about the baseline characteristics.