Don't Miss Vasculitic Myopathy Without Elevated Creatine Phosphokinase.

Area of Science:

• Rheumatology
• Neurology
• Pathology

Background:

• Vasculitic myopathy is an underrecognized complication of systemic vasculitis.
• Microscopic polyangiitis (MPA) is a form of ANCA-associated vasculitis.
• Muscle symptoms in vasculitis can be challenging to diagnose, especially when creatine phosphokinase (CPK) levels are normal.

Purpose of the Study:

• To describe a case of vasculitic myopathy secondary to MPA in an elderly woman.
• To highlight the diagnostic challenges posed by normal CPK levels in the presence of active myositis.
• To emphasize the importance of considering vasculitic myopathy in ANCA-associated vasculitis.

Main Methods:

• Case report of an 83-year-old woman presenting with subacute fever and lower limb pain.
• Diagnostic workup included magnetic resonance imaging (MRI) of the muscles and muscle biopsy.
• Histopathological examination of the muscle biopsy was performed.

Main Results:

• The patient was diagnosed with vasculitic myopathy due to MPA.
• MRI and muscle biopsy confirmed active muscle involvement.
• Histopathology revealed small-vessel vasculitis with fibrinoid necrosis and internal elastic lamina disruption.
• Creatine phosphokinase (CPK) levels remained normal throughout the evaluation.

Conclusions:

• Vasculitic myopathy can occur in MPA without elevated CPK levels.
• Normal CPK does not exclude active muscle inflammation in ANCA-associated vasculitis.
• Increased clinical suspicion and appropriate investigations are crucial for diagnosing this underrecognized condition.