From the Guidelines
Yes, complement C3 and C4 levels can be low in dermatomyositis, particularly in patients with active disease or overlap syndromes with other connective tissue diseases. Dermatomyositis is an inflammatory myopathy characterized by muscle weakness and skin manifestations. In some patients with dermatomyositis, complement consumption occurs as part of the autoimmune inflammatory process, leading to decreased serum levels of complement components, including C3 and C4 1. Low complement levels may indicate more severe disease activity and can be used as one of several markers to monitor disease progression and response to treatment. However, it's essential to note that not all patients with dermatomyositis will have low complement levels, and normal complement levels do not exclude the diagnosis. Other laboratory findings in dermatomyositis typically include elevated muscle enzymes (CK, aldolase), positive myositis-specific antibodies, and inflammatory markers like ESR and CRP.
Key Points to Consider
- Complement consumption can occur in dermatomyositis, leading to low C3 and C4 levels 1
- Low complement levels are more commonly seen in patients with overlap syndromes or active disease
- Complement levels can be used as a marker to monitor disease progression and response to treatment
- Other laboratory findings, such as elevated muscle enzymes and inflammatory markers, are also important in diagnosing and managing dermatomyositis
Management and Treatment
The management of dermatomyositis involves a multidisciplinary approach, including the use of immunosuppressive therapy, such as methotrexate, azathioprine, or mycophenolate mofetil, in addition to corticosteroids 1. The treatment approach may vary depending on the severity of the disease and the presence of overlap syndromes. Close monitoring of patients' disease status and well-being is essential for a good clinical outcome. Recent evidence highlights the importance of treating skin disease aggressively, as it is associated with high morbidity 1.
Monitoring and Follow-up
Validated scores for disease activity and damage are needed to perform a structured assessment of outcome 1. Disease activity and damage scores have been developed, principally for clinical trials, but may be challenging and time-consuming to use in daily clinical practice. Long-term follow-up studies are warranted to clarify complication risks, and international collaboration is crucial to recruit sufficient patients 1.
From the Research
Complement C3 and C4 Levels in Dermatomyositis
- Complement C4 levels can be low in dermatomyositis, as studies have shown that low copy numbers of complement C4 and C4A deficiency are risk factors for myositis, including dermatomyositis 2.
- C4A deficiency is particularly relevant in dermatomyositis, and patients with this deficiency have been found to have lower C4 plasma concentrations and higher levels of processed activation product C4d bound to erythrocytes (E-C4d) 2, 3.
- While there is no direct evidence on Complement C3 levels in dermatomyositis, studies have shown that complement activation, including the classical complement pathway, plays a role in the pathogenesis of dermatomyositis 4, 5.
- Microvascular alterations and complement activation are features of dermatomyositis pathology, and C4d expression can be used as a marker of complement activation in the diagnosis of dermatomyositis 4, 5.
Studies on Complement Levels in Dermatomyositis
- A study on dogs with familial canine dermatomyositis found no absolute complement component deficiency, but a statistical difference in C2 was identified between control dogs of non-collie breeds and control collies 6.
- A study on juvenile dermatomyositis found that complement C4A deficiency is an important factor for the genetic risk and pathogenesis of the disease, particularly in patients with a DR3-positive background 3.
- Another study found that perifascicular atrophy in dermatomyositis is consistently associated with focal microvascular depletion, and that microvascular membrane attack complex deposits in dermatomyositis result from activation of the classical complement pathway 5.