Anti-NXP2 is considered specific for dermatomyositis. Less frequently it be associated with polyarthritis without myositis or rash.
NXP2 = antinuclear matrix protein
NOTE: Polyarthritis can occur in dermatomyositis with myositis and rash due to anti-NXP2.
Clinical features:
(1) polyarthritis
(2) absence of myositis and rash
(3) nailfold capillaroscopy positive for dystrophic capillaries
Laboratory features:
(1) ANA positive, with apeckled or diffuse patterns
(2) anti-NXP2 positive
(3) rheumatoid factor negative
(4) normal serum CK concentrations
(5) normal serum inflammatory markers (CRP, ESR)
Imaging studies:
(1) normal MRI
It is prudent to monitor the patient for an underlying malignancy.
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Specialty: Immunology/Rheumatology
