From the Guidelines
The most appropriate test to order next for this 41-year-old man is serum antinuclear antibody level (option E). This patient's presentation strongly suggests dermatomyositis, an inflammatory myopathy characterized by proximal muscle weakness and distinctive skin findings, as described in the guidelines for managing immune-related adverse events 1. The clinical picture includes the classic heliotrope rash (violaceous rash over the eyelids), Gottron's papules (erythematous patches over the metacarpal joints), and mechanic's hands (cracking of the skin at fingertips), along with progressive proximal muscle weakness affecting the quadriceps and shoulders.
Key Considerations
- Serum antinuclear antibody testing is an appropriate initial step in the diagnostic workup for inflammatory myopathies like dermatomyositis, as these autoimmune conditions often show positive ANA results, according to the American Society of Clinical Oncology clinical practice guideline 1.
- This test can help confirm the autoimmune nature of the disease before proceeding to more invasive testing like muscle biopsy.
- While muscle biopsy would be definitive, it's reasonable to start with less invasive serologic testing.
- Other tests such as CK, transaminases (AST, ALT), LDH, and aldolase can also be considered to evaluate muscle inflammation, as well as inflammatory markers (ESR and CRP) 1.
Ruling Out Other Options
- The other options (lumbar puncture, MRI of lumbar spine, and anti-acetylcholine receptor antibody) are not indicated as first-line tests for the clinical presentation of dermatomyositis.
- Consideration of preexisting conditions that can cause similar symptoms and differential diagnosis is important, but the presentation here points more directly towards an inflammatory myopathy like dermatomyositis 1.
From the Research
Diagnostic Approach
The patient presents with a 3-week history of a rash on his hands and elbows, progressive weakness in his lower extremities and shoulders, and difficulty walking up stairs. The physical examination reveals erythematous patches, a violaceous rash, cracking of the skin, and increasing discomfort on reaching his upper extremities above the head. Given these symptoms, the most likely diagnosis is dermatomyositis.
Relevant Tests
To confirm the diagnosis, the following tests can be considered:
- Muscle biopsy: This is a definitive test for diagnosing dermatomyositis, as it can show characteristic myopathologic features such as perifascicular atrophy and perifascicular myxovirus resistant protein A (MxA) overexpression 2.
- Electromyography: This test can show abnormal muscle activity, which is consistent with dermatomyositis 3.
- Magnetic resonance imaging (MRI) of the involved muscle: This test can show muscle inflammation and damage, which is consistent with dermatomyositis 3.
- Serum antinuclear antibody (ANA) level: This test can help diagnose dermatomyositis, as many patients with this condition have a positive ANA 4.
- Serum myositis-specific antibody (MSA) level: This test can help diagnose dermatomyositis and guide treatment, as different MSAs are associated with different disease courses and treatment responses 2, 5, 4.
Most Appropriate Test
Based on the patient's symptoms and physical examination, the most appropriate test to order next would be:
- E. serum antinuclear antibody level: This test is a good initial test to help diagnose dermatomyositis, as many patients with this condition have a positive ANA. Additionally, the patient's symptoms and physical examination are consistent with dermatomyositis, and an ANA test can help confirm this diagnosis 4.
Alternatively, a muscle biopsy could be considered, as it is a definitive test for diagnosing dermatomyositis 2. However, this test is more invasive than an ANA test, and an ANA test may be a good initial step to help guide further diagnosis and treatment.