musculoskeletal and connective tissue disorders
Polyarteritis Nodosa (PAN)
Diagnosis of PAN
Clinical findings Biopsy Arteriography if no clinically involved tissue is available for biopsy PAN can be difficult to diagnose because findings can be nonspecific. The diagnosis should be considered in patients with various combinations of symptoms, such as unexplained fever, arthralgia, subcutaneous nodules, skin ulcers, pain in the abdomen or extremities, new footdrop or wristdrop, or rapidly developing hypertension. The diagnosis is further clarified when clinical findings are combined with certain laboratory results and other causes are excluded. Diagnosis of polyarteritis nodosa is confirmed by biopsy showing necrotizing arteritis or by arteriography showing the typical aneurysms in medium-sized arteries. Magnetic resonance angiography may show microaneurysms, but some abnormalities may be too small for it to detect. Thus, magnetic resonance angiography is not the test used primarily for diagnosis. Biopsy of clinically uninvolved tissue is often useless because the disease is focal; biopsy should target sites suggested by clinical evaluation. Samples of subcutaneous tissue, sural nerve, and muscle, if thought to be involved, are preferred to samples from the kidneys or liver; kidney and liver biopsies may be falsely negative because of sampling error and may cause bleeding from unsuspected microaneurysms. Unlike in granulomatosis with polyangiitis (GPA), biopsy is unlikely to show marked parenchymal inflammation. If clinical findings are absent or minimal, electromyography and nerve conduction studies may help select the site of muscle or nerve biopsy. If skin lesions are present, surgical skin biopsies that include deeper dermis and subcutaneous fat should be done. (Punch biopsies of the skin that sample the epidermis and superficial dermis miss the lesions of PAN.) Even though microscopic lesions in the testes are common, testicular biopsy should not be done if testicular symptoms are absent and if other possible sites are accessible because the yield is low. Also, men may be reluctant to have testicular biopsy. Laboratory tests are nonspecific. Leukocytosis up to 20,000 to 40,000/microL (20 to 40 × 109/L), proteinuria, and microscopic hematuria are the most common abnormalities. Patients may have thrombocytosis, markedly elevated erythrocyte sedimentation rate, anemia caused by blood loss or renal failure, hypoalbuminemia, and elevated serum immunoglobulins. Aspartate aminotransferase and alanine aminotransferase are often mildly elevated. Testing for hepatitis B and C should be done. Because glomerulonephritis is not a feature of PAN, red blood cell casts are not evident on urinalysis. Other testing (eg, antineutrophil cytoplasmic antibodies [ANCA], rheumatoid factor, anticyclic citrullinated peptide [anti-CCP] antibody, antinuclear antibodies [ANA], C3 and C4 complement levels, cryoglobulin levels, nuclear antigens and antibodies to extractable nuclear antigens such as anti-Smith, anti-Ro/SSA, anti-La/SSB, and anti-RNP) may suggest other diagnoses, such as rheumatoid arthritis, systemic lupus erythematosus, or Sjögren syndrome. 