Investigations

1st investigations to order

CRP

Test
Result
Test

CRP is an acute phase protein that is elevated in most inflammatory conditions. A normal CRP level would argue against a diagnosis of polyarteritis nodosa (PAN).

Result

elevated

erythrocyte sedimentation rate (ESR)

Test
Result
Test

ESR is raised in inflammatory conditions, including PAN.

Result

elevated

FBC

Test
Result
Test

A normochromic, normocytic anaemia is a common feature of inflammation and, therefore, a frequent finding in PAN. Neutrophilia or eosinophilia may be present. A raised platelet count is a recognised feature. In contrast, a low platelet count may indicate other disease processes such as systemic lupus erythmatosus (SLE) or catastrophic antiphospholipid syndrome.

Result

normocytic anaemia, mildly elevated WBC count, raised platelet count

complement

Test
Result
Test

Activation of the complement cascade by immune complexes (especially in hepatitis B virus [HBV]-related PAN) may result in low complement levels.

Result

reduced

serum creatinine

Test
Result
Test

PAN can affect the renal arteries and cause renal ischaemia or infarction with a resulting rise in serum creatinine.

Result

elevated or normal

midstream urine analysis

Test
Result
Test

Urinalysis is useful to rule out infection and exclude glomerulonephritis. PAN does not cause glomerulonephritis, and the presence of red cell casts or severe proteinuria suggests an alternative diagnosis such as granulomatosis with polyangiitis (GPA, formerly known as Wegener's granulomatosis) or microscopic polyangiitis (MPA).

Result

mild proteinuria or normal

liver function tests

Test
Result
Test

Mild elevation of liver enzymes is common. Acute hepatitis is possible during initial infection with HBV or may be a result of ischaemic hepatitis.

Result

elevated liver enzymes

HBV serology

Test
Result
Test

HBV infection typically occurs a few months before the development of HBV-related PAN.

Result

HbsAg positive and/or HbeAg positive

hepatitis C virus (HCV) serology

Test
Result
Test

HCV infection is associated with a predominantly cutaneous form of PAN.

Result

positive anti-hepatitis C antibodies

cryoglobulins

Test
Result
Test

Presence of cryoglobulins would suggest an alternative diagnosis. Cryoglobulins are strongly associated with hepatitis C virus infection and can cause a small-vessel vasculitis.

Result

no cryoglobulins

blood culture

Test
Result
Test

It is important to exclude endovascular infection, which can mimic vasculitis, especially before embarking on immunosuppressive therapy.

Result

no growth of organisms

creatine kinase

Test
Result
Test

Creatine kinase is not markedly elevated in PAN, even when there is muscle involvement.

Result

normal or mildly elevated

anti-neutrophil cytoplasmic antibodies (ANCA)

Test
Result
Test

PAN is not associated with ANCA. A positive result in the context of suspected vasculitis would suggest an alternative type of vasculitis.

Result

negative

antinuclear antibodies (ANA)

Test
Result
Test

Can be a useful test in the right context. A positive ANA may help to point towards an alternative diagnosis such as SLE or another connective tissue disorder.

Result

negative

anti-double-stranded DNA antibodies (anti-dsDNA)

Test
Result
Test

A positive result for anti-dsDNA can be useful to make a diagnosis of SLE if manifestations fit with this diagnosis.

Result

negative

rheumatoid factor

Test
Result
Test

Useful only if rheumatoid arthritis is a possible alternative diagnosis on the basis of the history and examination.

Result

negative

antibodies to cyclic citrullinated peptides (anti-CCP antibodies)

Test
Result
Test

Useful only if rheumatoid arthritis is a possible alternative diagnosis based on the history and examination.

Result

negative

lupus anticoagulant

Test
Result
Test

May be present in antiphospholipid syndrome.

Result

negative

immunoglobulin G antiphospholipid antibodies

Test
Result
Test

May be present in antiphospholipid syndrome.

Result

negative

B2 glycoprotein

Test
Result
Test

May be present in antiphospholipid syndrome.

Result

negative

fibrinogen

Test
Result
Test

Fibrinogen may be elevated in PAN as a marker of acute inflammation. It may be low in catastrophic antiphospholipid syndrome.

Result

normal or elevated

conventional digital subtraction angiography

Test
Result
Test

This is the standard method of imaging potentially affected vessels. The sensitivity and specificity of the test in a selected population suspected of vasculitis is 89% and 90%, respectively.[40] The main disadvantage is that it is a relatively invasive procedure.

Result

microaneurysms, vessel ectasia, or focal occlusive lesions in medium-sized vessels

echocardiography

Test
Result
Test

Useful to exclude an alternative diagnosis such as endocarditis, atrial myxoma, or a left ventricular thrombus.

Result

normal

Investigations to consider

magnetic resonance angiography (MRA)

Test
Result
Test

MRA is a non-invasive method of imaging potentially affected vessels, but it has lower spatial resolution than conventional angiography and is not very good at detecting microaneurysms.[41] It has the benefit of being able to show areas of organ infarction.

In patients with normal MRA and suspected PAN, conventional angiography is indicated.

Result

aneurysms or focal occlusive lesions of medium-sized vessels

CT angiography

Test
Result
Test

CT angiography is a non-invasive alternative to MRA and conventional angiography. It has better spatial resolution than MRA, but it is not as good as conventional angiography at detecting microaneurysms.[41] It has the benefit of being able to show areas of organ infarction.

In patients with normal CT angiography and suspected PAN, conventional angiography is indicated.

Result

aneurysms or focal occlusive lesions of medium-sized vessels

biopsy of affected tissue

Test
Result
Test

The tissue sampled must be targeted from the history and examination. Muscle, peripheral nerves, kidney, testis, and rectum, when involved, provide the best targets. A positive skin biopsy does not always suggest systemic involvement.[Figure caption and citation for the preceding image starts]: Pathology specimen of a medium-sized muscular artery showing transmural inflammationFrom the collection of Dr Raashid Luqmani [Citation ends].com.bmj.content.model.Caption@4d686df5[Figure caption and citation for the preceding image starts]: Biopsy specimen showing florid transmural inflammation of a small arteryFrom the collection of Dr Loic Guillevin [Citation ends].com.bmj.content.model.Caption@59a72ee6

Result

focal and segmental transmural necrotising inflammation in a medium-sized vessel (i.e., a small- or medium-sized artery)

HIV serology

Test
Result
Test

It is important to rule out HIV infection, which is a cause of vasculitis in its own right.

Result

negative

genetic test for adenosine deaminase 2 (ADA2) deficiency

Test
Result
Test

Consider testing for lack of function mutations in the adenosine deaminase 2 gene (previously called the CECR1 gene) in young patients presenting with classical features of PAN, especially if stroke is part of the presentation.

Result

The test is negative in idiopathic PAN. However deficiency of adenosine deaminase 2 (DADA2) is a recently described monogenic vasculitis syndrome and some patients previously diagnosed with PAN likely had DADA2.

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