Can creatine kinase (CK) levels be normal in patients with dermatomyositis?

Can CK Be Normal in Dermatomyositis?

Yes, CK can be normal in dermatomyositis, particularly in amyopathic and hypomyopathic subtypes where patients present with characteristic skin manifestations but minimal or no muscle enzyme elevation.

Clinical Context and Subtypes

Dermatomyositis exists on a spectrum, and CK levels vary significantly depending on the subtype:

Amyopathic Dermatomyositis

• Patients present with classic DM rash without evidence of muscle inflammation, characterized by normal muscle enzyme levels within 2 years after diagnosis and normal EMG findings 1
• This represents a well-recognized clinical entity where CK remains within normal limits throughout the disease course 1

Hypomyopathic Dermatomyositis

• Patients lack muscle weakness but may show evidence of muscle inflammation with only mild CK elevation 1
• Abnormalities may be detected on EMG, MRI of proximal muscles, or muscle biopsy despite minimal enzyme elevation 1

Classic Dermatomyositis

• While most patients with classic DM have elevated CK, rare cases exist with normal CK throughout the entire clinical course 2, 3
• A documented case demonstrated Gottron's papules, heliotrope rash, cutaneous ulcers, generalized weakness, and interstitial lung disease with persistently normal CK levels 2

Diagnostic Approach When CK is Normal

When evaluating suspected dermatomyositis with normal CK:

Measure Multiple Muscle Enzymes

• Check CK, AST, ALT, LDH, and aldolase, as one enzyme may be elevated when CK is normal or only mildly elevated 4, 5
• This multi-enzyme approach increases diagnostic sensitivity 4

Consider Autoantibody Testing

• Anti-melanoma differentiation-associated gene 5 (anti-MDA5) antibodies are associated with clinically amyopathic dermatomyositis and do not present with raised CK 2
• Anti-small ubiquitin-like modifier 1 (anti-SUMO-1) activating enzyme antibodies also correlate with normal CK presentations 2

Advanced Imaging and Electrophysiology

• MRI can detect muscle inflammation even when CK is normal 1
• EMG may show myopathic changes despite normal enzyme levels in hypomyopathic variants 1
• Muscle biopsy remains the gold standard when diagnosis is uncertain 1

Critical Clinical Pitfalls

Do Not Exclude Dermatomyositis Based on Normal CK Alone

• The absence of CK elevation does not rule out dermatomyositis, particularly in amyopathic variants 1, 2
• Relying solely on CK can lead to missed diagnoses and delayed treatment 2

Screen for Associated Complications

• Interstitial lung disease occurs in amyopathic DM and may be present despite normal CK 1, 2
• Malignancy screening remains important, though the incidence is lower in amyopathic DM compared to classic DM 1
• The historical suggestion that normal CK predicts poor prognosis and higher malignancy risk has been challenged by more recent case reports 3

Distinguish from Polymyalgia-Like Syndromes

• Polymyalgia rheumatica presents with pain but not true weakness, and CK should remain normal 4, 5
• This serves as a key differentiating feature from true myositis 4

Treatment Implications

Even with normal CK, patients with dermatomyositis require immunosuppressive therapy:

• Standard treatment includes oral corticosteroids, hydroxychloroquine, and steroid-sparing agents like mycophenolate or methotrexate 2
• The treatment approach should be guided by clinical manifestations (skin disease, weakness, systemic involvement) rather than CK levels alone 2
• Response to therapy may be monitored through clinical improvement in skin manifestations and functional status, not just enzyme normalization 2