ABSTRACT
Fever of unknown origin (FUO) is uncommonly due to rheumatic or collagen vascular diseases. Petersdorf, in his classic 1961 description of FUOs, described the various etiologies of prolonged undiagnosed fever. At that time, infectious diseases were the most common cause of FUO followed by malignancy, and the next most common category was that of collagen vascular diseases. Since 1961, there have been a variety of serological diagnostic tests helpful in the diagnosis of most collagen vascular diseases. The result has been that collagen vascular diseases are a relatively uncommon cause of FUO at the present time (1). Rheumatic diseases such as rheumatoid arthritis (RA) and systemic lupus erythematosus (SLE) are rare causes of FUO because of the many serological tests currently available to diagnose these disorders. The collagen vascular diseases that continue to be diagnostic problems, presenting as FUOs include those which are not readily diagnosable by simple or specific diagnostic tests. At the present time, collagen vascular diseases that are likely to remain undiagnosed after one month of fever and one week of inpatient/outpatient diagnostic testing include Kikuchi’s disease, Takayasu’s arteritis, late onset rheumatoid arthritis (LORA), polymyalgia rheumatica (PMR), temporal arteritis (TA), vasculitides, for example, periarteritis nodosa (PAN), and adult juvenile rheumatoid arthritis (JRA) also known as adult onset Still’s disease (1,2).
