Vasculitis

Dr Simon Carette took us through the approach to vasculitis as we discussed a patient with a case of Microscopic Polyangiitis (MPA).

This patient presented with mononeuritis multiplex as well as purpura of the legs.

Some pearls that he shared:

1) Mononeuritis multiplex: dysfunction of multiple named peripheral nerves. Pathognomonic for vasculitis. The most common causes are:
- Polyarteritis Nodosa
- Churg-Strauss Syndrome
- Cryoglobulinemia
- Connective Tissue Disease-Associated (note that not all CTDs cause vasculitis- the ones that do most commonly are lupus, rheumatoid arthritis and Sjogren's).

Mononeuritis mulitplex could, for example, present as an isolated foot drop. One important question when examining these patients is: how to distinguish a common peroneal nerve palsy  from an L5 radiculopathy (both cause foot drop).
Key distinction: Ankle inversion and thigh abduction are weak in L5 radiculopathy, but not in common peroneal nerve palsy. Weak dorsiflexion and eversion are seen in both conditions.

2) Skin lesions in vasculitis: presentation depends on which vessels are involved.
- Small vessel vasculitis- superficial vessels involved= petechiae, purpura (see lower image above), hemorrhagic bullae.
- Medium-sized vessel vasculitis- depper vessels involved= livedo reticularis (classic in PAN, see top image above), nodules, ulcers. Note that a standard punch biopsy will not reach the deeper layers and miss the diagnosis. In the presence of these skin lesions, a deeper punch or wedge biopsy is needed.

3) ANCA Antibody Testing:
- c-ANCA highly specific for anti-PR3 antibody and Granulomatosis and Polyangiitis (previously known as Wegener's)
- p-ANCA much less specific for anti-MPO- thus positivity on p-ANCA testing should prompt a follow-up ELISA test for anti-MPO (many other things including IBD can give you a positive p-ANCA that are not associated with vasculitis). If anti-MPO positive, 80% specific for a vasculitis (MPA, Churg-Strauss)


Finally, check out this NEJM CPC case on PAN for a good review of the approach to a patient with vasculitis.