A study of the utility of azathioprine metabolite testing in myasthenia gravis

• Azathioprine remains a first line broad acting immunosuppressant for myasthenia.
• Azathioprine metabolites in myasthenia gravis have not been investigated before.
• Correlations between symptoms, 6-TGN and lymphocytes were identified.
• Azathioprine metabolites may be considered in patients with treatment complications.

Myasthenia gravis (MG) is an autoimmune neuromuscular disorder characterised by fatigable voluntary skeletal muscle weakness. The underlying pathogenesis is complex involving adaptive autoimmune responses. Azathioprine remains a first line broad acting immunosuppressant for MG. Due to varied clinical responses to azathioprine we aimed to investigate the relationship between azathioprine metabolites and symptom control. Mild correlations between Quantitative Myasthenia Gravis Score (QMG) vs. 6-thioguanine nucleotides (R = − 0.317 p = 0.186) and QMG vs. lymphocyte count (R = 0.402 p = 0.08) were found. Azathioprine metabolite measurement should be considered in MG patients with; pancytopenia, deranged liver function or recurrent infections.

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