Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (28 page)

   Laboratory Findings

Diagnosis is based on clinical findings and the history of offending drug treatment or infection. Skin biopsy typically shows leukocytoclastic vasculitis.

   Decreased complement levels and increased ESR are present.

   Presence of mixed cryoglobulinemia in the serum can be found in patients chronically infected with hepatitis C virus.

POLYARTERITIS NODOSA

   Definition

   This systemic necrotizing arteritis affects medium-sized muscular arteries, with occasional involvement of small muscular arteries.

   See Table
2-1
.

   Who Should Be Suspected?

   Candidates are middle-aged or elderly individuals presenting with nonspecific symptoms of fatigue, arthralgias, weakness, or fever. These symptoms can be associated with signs of multisystem involvement such as hypertension, renal insufficiency, neurologic dysfunction, skin lesions, muscle involvement, or abdominal pain.

   The condition is more common in men than women and may be preceded by hepatitis B or C infection.

   Laboratory Findings

Diagnosis is based on clinical manifestations and confirmed by biopsy of involved organs. Laboratory studies are not diagnostic.

   Elevated ESR and CRP.

   Serologic tests are useful to rule out other autoimmune disorders and narrow down the differential diagnosis. ANCA test is usually negative in polyarteritis nodosa patients.

TAKAYASU ARTERITIS

   See Chapter
3
, Cardiovascular Disorders.