26th January 2024

Management

Dermatomyositis and Polymyositis 

Systemic glucocorticoids are the mainstay of acute treatment. Patients are started on a tapering dose usually for one year, which improves the strength and preservation of muscle function. 

A glucocorticoid-sparing agent is started simultaneously as the Prednisolone is weaned off. Azathioprine is frequently used and is usually started at a dose of 50mg/day. Prior to initiating Azathioprine, it is important to check for thiopurine methyltransferase deficiency (TPMT) deficiency, as these patients would be at significant risk of having myelosuppression and neutropenic sepsis on Azathioprine. Regular monitoring of liver function tests and complete blood count is done every three months. 

Methotrexate is also used as a steroid-sparing agent and is generally started at 15mg once weekly dosing and is titrated up. Folic acid is administered with Methotrexate to prevent folate deficiency, which can have symptoms such as mouth ulcers, paresthesia, fatigue, and muscle weakness. Methotrexate can have other adverse effects such as methotrexate pneumonitis and methotrexate toxicity. 

Antimalarials such as Hydroxychloroquine can be used to help to control skin disease. However, it is not beneficial for muscle disease. 

Inclusion body myositis 

The management of inclusion body myositis primarily aims to optimise muscle strength and function. Non-pharmacological interventions which have proven to be helpful include physiotherapy and speech therapy. Physiotherapy can provide a tailored exercise program, and with the assistance of occupational therapy, appropriate assistive devices can be sourced. 

It is not generally recommended to use immunosuppressive therapy in inclusion body myositis. However, in some cases, particularly where there is suspicion of overlap with another autoimmune disease, a trial of Prednisolone can be done, and if there is a response, consideration may be given to tapering prednisolone and commencing a steroid-sparing agent such as azathioprine or methotrexate.