• Quotidian fever, frequently >39°C.
  
• Evanescent, salmon-colored macular rash on trunk and extremities, often coincident with fever spikes.
  
• Clinical manifestations include pharyngitis, polyarthralgias, lymphadenopathy, splenomegaly, and serositis.
  
• Leukocytosis and elevations of the erythrocyte sedimentation rate, serum C-reactive protein, and serum ferritin are common laboratory abnormalities.

Adult-onset Still disease (AOSD) is a multisystem inflammatory disease of unknown cause. It affects women and men equally and is rare, with a reported incidence of 0.16 cases per 100,000 in one series. AOSD typically begins in the late teenage to early adult years, but disease onset occurs after the age of 35 in approximately 25% of patients. The onset of AOSD is systemic, with fever and rash; however, the subsequent disease course is variable. AOSD may consist of single (monocyclic) or recurrent (polycyclic) episodes of systemic disease lasting weeks to months. Alternatively, chronic articular disease, with or without recurrent systemic flares, may follow the initial systemic episode. Pediatric patients with systemic-onset juvenile idiopathic arthritis can have a recurrence of active Still disease at any age into adulthood. There are no definitive laboratory findings or diagnostic histologic abnormalities. The diagnosis is made on clinical grounds and often is one of exclusion (Table 16–1).

Symptoms and Signs

Fever

Fever is a hallmark of AOSD. Typically, the fever is quotidian, with spikes to ≥39°C (often in the afternoon or evening) followed by return to normal temperature in the absence of antipyretic medications. Shaking chills and sweating can accompany these daily temperature swings, which can be as high as 4°C. Occasionally, the fever is double quotidian (two spikes daily). In a small percentage of patients, a low-grade baseline fever persists between spikes. Untreated, the fever of AOSD is relentless, frequently lasting weeks at a time. Constitutional symptoms of profound fatigue, weight loss, and anorexia are common.

Rash

The rash of AOSD is a salmon-colored, macular or maculopapular eruption (Plate 34). Occasionally, it has an urticarial appearance. The rash usually affects the trunk and the extremities and spares the face, palms, and soles. It is evanescent, often appearing during febrile episodes and then clearing when the temperature returns to normal. The rash of AOSD usually is asymptomatic, but it may be mildly pruritic. Scratching uninvolved skin can elicit the rash (Koebner phenomenon). Biopsy of involved skin reveals a neutrophilic infiltration of the dermis and perivascular spaces; these histologic findings are not specific for AOSD and can be seen with urticaria of any cause, cellulitis, and other conditions.

Pharyngitis

A sore throat due to nonsuppurative pharyngitis is often the earliest symptom of AOSD and may precede fever, rash, and arthralgias by days to weeks.

Arthritis