PAN/Polyarteritis nodosa
Polyarteritis nodosa (aka PAN) is a vasculitis that affects medium (and small) arteries. Along with Kawazaki disease, it is one of two medium blood vessel vasculitis. Unsurprisingly, its aetiology is unknown, as is its pathophysiology….really rheumatologists need to start doing some research! What we do know is that it is a necrotising vasculitis that causes aneurysms and thrombosis in medium sized arteries leading to infarction of affected vessels.
PAN has a predilection for the skin, peripheral nerves, GI tract and kidneys. The disease usually starts with nonspecific symptoms such as malaise, fatigue, fever, myalgias and arthralgias. After weeks, or months, skin lesions will begin to develop with features such as livedo reticularis (purple lattice like skin discolouration), subcutaneous nodules, ulcers and distal gangrene. Over 80% of patients will have vasculitic neuropathy.
Image: “Livedo reticularis” by డా. గన్నవరపు నరసింహమూర్తి, CC0, via Wikimedia Commons.
The GI manifestation is that of postprandial abdominal pain, while the renal manifestation is renin-mediated hypertension and renal infarctions. Cardiac lesions may occur, but these are usually subclinical, in rare occurrences it may lead to an MI or congestive heart failure. Polyneuropathic symptoms may also occur and lead to increased suspicion of PAN.
Diagnosis is based on tissue biopsy or an angiogram which demonstrates microaneurysms.
Polyarteritis nodosa affects all of the layers of the blood vessel (PAN arteritis). What we know of the pathogenesis is that T Helper cells are activated by an antigen (thought to be some infectious agent) which stimulates an immune response, with neutrophils infiltrating the vessel wall, and causing inflammation. Following this inflammation, macrophages enter the wall to repair the inflamed tissue, in doing so they lay down fibrous tissue. This creates what is known as fibrinoid necrosis. This fibrinoid necrosis occurs in segments along the vessel, and weakens the vessel wall, leaving it open for an aneurysm to occur. Macroscopically (on an angiogram) the vessels will look something like beads on a string which is diagnostic for PAN.
Patients with Hep B can often present with polyarteritis nodosa, and all PAN patients should be screened for Hep B.
The rash in PAN can be numerous things, including:
- Purpuric rash
- Subcutaneous nodules
- Bullous/vesicular lesions
- And livedo reticularis (that was described earlier)
Around 50% of patients achieved remission with high doses of glucocorticoids (prednisolone 1mg/kg/day; cyclophosphamide 2mg/kg/day is added in severe disease) - this is first line treatment.