Background: Limb restricted polyarteritis nodosa (PAN) and PAN-type diseases such as isolated vasculitis of skeletal muscle are localised vasculitides affecting the skin, muscles, or peripheral nerves, usually of the lower limbs. These diseases often present with non-specific clinical symptoms and normal laboratory values and electromyograms. The usefulness of magnetic resonance imaging (MRI) of skeletal muscle has been poorly investigated to date.
Objective: To describe the MRI findings in the legs of three patients with limb restricted vasculitides (two PAN, one isolated vasculitis of the skeletal muscle) with histologically established muscle involvement.
Methods: MRI was carried out on calf muscles and T(2) weighted images, unenhanced T(1) weighted images, and STIR sequences were obtained.
Results: Muscle damage resulted in oedema-like changes on MRI characterised by hyperintense signals in T(2) weighted and slow tau inversion recovery (STIR) sequences and normal unenhanced T(1) weighted sequences of one or several leg muscles.
Conclusions: MRI should be considered a useful complementary examination that might facilitate the recognition of limb restricted vasculitides, and possibly indicate the site for muscle biopsy. It could also be useful in monitoring the course of the disease. Future studies should also evaluate MRI for systemic PAN or other systemic vasculitides with muscle involvement.