Definition
Inflammatory myositis is the name for a group of autoimmune disorders characterized by immune-mediated damage to skeletal muscle.
Major subtypes are:
- Inclusion body myositis
- Immune mediated necrotising myositis
- Dermatomyositis
- Antisynthetase syndrome
- Overlap myositis with other connective tissue diseases such as lupus, systemic sclerosis.
History
- Proximal muscle weakness causing difficulty rising from a chair, getting out of the car, climbing stairs, lifting objects and combing hair associated with fatigue, myalgia
- Onset over weeks to months and steady progression
Associated Systemic features:
- Pharyngeal muscle(dysphagia) or laryngeal muscle(dysphonia) or respiratory muscle weakness may also be present
- Chronic dry cough with breathlessness (CXR – features of interstitial lung disease)
- Symptoms of connective tissue disease such as Raynaud’s, sicca symptoms, photosensitive rash, serositis, inflammatory arthritis
- Weight loss
- Distinctive skin rash:
- Gottron papules on the dorsal aspect of the hands and fingers
- Periorbital oedema and erythema of the face (heliotrope rash)
- Rash on the anterior upper chest (V-sign) or the posterior neck (shawl sign)
- Periungual erythema and telangiectasia
- Thickened and cracked skin of acral surface of the fingers (mechanic’s hand)
Investigation
- Creatine kinase- raised (CK can be normally up to 5 times upper limit normal)
- Inflammatory markers – raised
- Abnormal liver function test (high ALT can be seen with raised CK)
- Autoimmune antibodies – ENA, ANA, CCP
- Malignancy screen if suspected (e.g. CT chest, abdomen, Pelvis) – association of malignancy with myositis
M.A & H.B/S.R – 29-7-26
When to refer :
Patients who meet all the criteria listed below should be referred urgently to rheumatology:
- elevated inflammatory markers and/or typical rash (as above)
- acute or sub-acute onset of symmetrical proximal muscle weakness
- elevated creatine kinase (CK > 5 Upper Limit Normal)
Who not to refer:
- Elevated CK without above clinical features – Consider an alternative diagnosis (See reference 1)
- Patients with diffuse myalgia with normal creatine kinase (up to 5 x ULN) and normal inflammatory markers
How to refer to Rheumatology:
- Urgent referral via SCI referral system
- SCI Gateway > Rheumatology > WGH
- Discuss with on-call via page for consideration of hospital admission if patient has pharyngeal/laryngeal/ respiratory muscle weakness
References:
1. Kim E J, Wierzbicki A S. Investigating raised creatine kinase BMJ 2021; 373:n1486 doi:10.1136/bmj.n1486 available at https://doi.org/10.1136/bmj.n1486
2. https://www.nejm.org/doi/full/10.1056/NEJMra2415426
