Differential Diagnosis for Elevated C3 and C4 with Myopathy
Single Most Likely Diagnosis
- Polymyositis or Dermatomyositis with Active Inflammation: Elevated C3 and C4 complement levels can be seen in active inflammatory conditions. Polymyositis and dermatomyositis are inflammatory myopathies that could present with myopathy and elevated complement levels due to the ongoing inflammatory process.
Other Likely Diagnoses
- Inclusion Body Myositis (IBM): Although IBM typically presents with slowly progressive weakness and may not always have significantly elevated inflammatory markers, some cases can have elevated C3 and C4 levels, especially if there's an overlap with other autoimmune conditions.
- Necrotizing Autoimmune Myopathy (NAM): This condition is characterized by muscle necrosis and can be associated with elevated complement levels. It often presents with rapid progression of weakness and can be associated with various autoantibodies.
- Thyroid-Associated Myopathy: Both hyperthyroidism and hypothyroidism can cause myopathy, and autoimmune thyroid diseases can lead to elevated complement levels due to the inflammatory nature of these conditions.
Do Not Miss Diagnoses
- Lupus Myositis: Systemic lupus erythematosus (SLE) can cause myositis, and patients with SLE often have elevated complement levels. Missing this diagnosis could lead to inadequate treatment of a potentially severe autoimmune condition.
- Vasculitis (e.g., Granulomatosis with Polyangiitis): Vasculitis can cause myopathy and elevated complement levels. These conditions can be severe and require prompt treatment to prevent organ damage.
Rare Diagnoses
- Eosinophilic Myopathy: A rare condition characterized by eosinophilic infiltration of muscles, which can be associated with elevated complement levels due to the inflammatory response.
- Sarcoid Myopathy: Sarcoidosis can rarely cause myopathy, and while complement levels might not be directly elevated by sarcoidosis, the condition's inflammatory nature could lead to elevated C3 and C4 in some cases.
- Mitochondrial Myopathies with Inflammatory Features: Some mitochondrial myopathies can have an inflammatory component, potentially leading to elevated complement levels, although this would be an uncommon presentation.