Key messages

• There is uncertainty if azathioprine improves or not muscular strength in polymyositis because the certainty of the evidence is very low.
• As far as we know there are no ongoing trials evaluating this question

What is the evidence.
See evidence matrix  in Epistemonikos later

We found one systematic review [1] including only one pertinent randomized controlled trial [2].

What types of patients were included

The study included adults with polymyositis diagnosed with Bohan and Peter criteria and positive muscle biopsy

What types of interventions were included

Azathioprine 2mg/kg qd plus prednisone 60 mg qd, compared with prednisone 60 mg qd.

What types of outcomes were measured

Improvement in muscular strength evaluated in each muscular group (score  from 0= no deficit, to -140= maximum deficit), serum creatine kinase, muscular biopsy (0= normal, to 36= maximum inflammation).

To whom this evidence does and does not apply

• The study included patients with polymyositis meeting Bohan and Peter criteria, so the evidence found is applied directly to this group. It is clinically reasonable to extend this findings to patients with dermatomyositis with muscular involvement. 
• It does not clearly apply to pediatric patients or patients with other rheumatologic diagnosis or presenting overlap syndrome.

• The outcomes presented are those considered critical for decision-making, according to the authors of this summary. We did not find clinical guidelines or studies about the relative importance of the outcomes for this condition. 

• It is not possible to estimate the risk/benefit given the existing uncertainty. Considering the intervention has side effects and costs its use outside of the context of a clinical trial is questionable.

• Given the absence of a clearly established alternative treatment, it is possible some clinicians will consider using this drug, especially in refractory patients. Some patients putting more value on the hypothetical benefit than on the risks and costs, may be inclined to use it too. In these cases, it is extremely important to inform the patient about the certainty of the evidence.  

• Given the uncertainty about the benefits, it is not possible to make a judgment about the cost/benefit.

Differences between this summary and other sources

• Our summary is in agreement with the only systematic review identified. 
• We did not identify guidelines that are recognized by a substantial proportion of experts in the topic.

• The probability of this information changing with new studies is very high because the certainty of the evidence is very low. 
• Unfortunately, we did not identify any ongoing study addressing this question.