Inflammatory Myopathies

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Original Editor - Lucinda hampton Top Contributors - Lucinda hampton, Rachael Lowe, Kim Jackson, Admin and Tony Lowe

Introduction

The idiopathic inflammatory myopathies (IIMs) are a group of rare, acquired disorders with primary features of muscle weakness and inflammatory lesions identified in skeletal muscle specimens.The three most mentioned of the idiopathic, immune-mediated varieties of IIMs are: dermatomyositis (DM), polymyositis (PM) and inclusion body myositis (IBM).

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Pathological Process, Incidence and Prevelance

Etiopathogenesis of these diseases is not fully understood. An autoimmune etiology of the IIMs is supported by the presence of serum autoantibodies, complement deposition in muscle tissue (in DM patients), lymphocyte-mediated cytotoxicity, and general clinical improvement in response to immunosuppression. Environmental triggers and genetic susceptibility are likely also involved with clear HLA gene associations and geographic case clusters. For example, HLA gene DRB1*0301 allele is associated with PM and IBM.

• The prevalence and incidence of these muscle diseases varies and is dependent on definitions and diagnostic criteria.
• Overall annual incidence rates for the IIMs vary from 2.18 to 7.7 per million
• Incidence rates also change with age and gender. There is a bimodal age distribution with peaks at age <15 and another between ages 45–54. There is a slight female predominance (F:M = 1.5:1.0)
• IBM is the most common subtype in men over the age of 50 .
• Under age 50, DM is more common than PM
• Incidence seems to be increasing, but this may reflect changes in disease awareness, medical billing codes, medical record technology, and more sensitive diagnostic tools.

Clinical Presentation

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Diagnostic Procedures

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Outcome Measures

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Management / Interventions Physiotherapy

A key component for treatment is an early rehabilitation program with the inclusion of strength-building and aerobic exercises, in addition to a rigorous evaluation of these activities for remission of disease and the education of the patient and his/her caregivers.

Physical and occupation therapy are essential and along with orthotic devices if needed. These help patients improve mobility, retain motor function, prevent contractures that can arise and may help prevent steroids side effects like weight gain, osteoporosis, and type 2 fiber atrophy.

• Strengthening programs twice weekly can be started as early as 2–3 weeks from the acute phase.
• With severe cases, passive range of motion exercises can be done for 3 months, until strength improve; at which point strengthening exercises are initiated. There is growing evidence for safety and beneficial effects of physiotherapy and home exercise programs in myositis .

A recent study demonstrated the effect of a 12-week aerobic exercise program in 10 children IMM's. At the end of this longitudinal study, the subjects showed an improvement in muscle strength and function, aerobic conditioning, and a better quality of life.

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Differential Diagnosis

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Key Evidence

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Resources

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Case Studies

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References

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