Dermatology MCQ - Inflammatory Dermatoses - Still disease

A 22-year-old woman presents to the emergency department with a spiking fever that peaks once daily in the late afternoon or evening, an evanescent, salmon-pink rash on her trunk and proximal extremities, and severe arthralgias. Laboratory studies show a leukocytosis with neutrophilia and a markedly elevated ferritin level. Which of the following is the most specific cutaneous finding for this disease?

A. A rash that appears with fever and disappears completely once the fever resolves
B. Fixed, violaceous plaques over the interphalangeal joints
C. A photosensitive malar rash
D. Urticarial papules and plaques with post-inflammatory hyperpigmentation
E. Subcutaneous nodules on the extensor surfaces

Correct Answer: A. A rash that appears with fever and disappears completely once the fever resolves

Explanation

This clinical picture is classic for Adult-Onset Still's Disease (AOSD). The rash of Still's disease is one of its most pathognomonic features.

• The Evanescent Rash: The classic rash of Still's disease is described as evanescent. It is a salmon-pink, macular or maculopapular eruption that typically appears coincidentally with the high-spiking fever and fades rapidly once the fever subsides. It is often distributed on the trunk and proximal extremities. This transient nature, coinciding with the fever spike, is highly specific for the disease.

Why other options are incorrect

• B. Fixed, violaceous plaques over the interphalangeal joints: This describes Gottron's papules, which are pathognomonic for dermatomyositis.

• C. A photosensitive malar rash: This is the hallmark of acute cutaneous lupus erythematosus.

• D. Urticarial papules and plaques with post-inflammatory hyperpigmentation: True urticaria is characterized by wheals that are transient but do not specifically correlate with fever cycles. Persistent urticarial lesions that leave hyperpigmentation are more suggestive of urticarial vasculitis.

• E. Subcutaneous nodules on the extensor surfaces: This is a classic finding in rheumatoid arthritis.

Key Associations for Still's Disease

• Pathogenesis: The etiology is unknown. It is considered an autoinflammatory disorder rather than a classic autoimmune disease, characterized by dysregulation of the innate immune system with massive IL-1, IL-6, and IL-18 production.

• Clinical Presentation (Yamaguchi Criteria): Diagnosis is often made using clinical criteria. Major criteria include:

  1. Fever ≥39°C, intermittent

  2. Arthralgia/Arthritis

  3. Characteristic rash

  4. Leukocytosis (≥10,000/μL with ≥80% granulocytes)
     The presentation described fits these criteria perfectly.

• Laboratory Findings: Key findings include a dramatically high leukocytosis with neutrophilia, a very high erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP), and an extremely elevated serum ferritin. A glycosylated ferritin level of <20% is highly specific for AOSD.

• Differential Diagnosis: The main differentials include sepsis, lymphoma, other autoimmune diseases (SLE, vasculitis), and hereditary autoinflammatory syndromes.

• Management & Prognosis:

  • First-line: NSAIDs may be sufficient for mild disease. Corticosteroids (e.g., prednisone) are the mainstay for moderate to severe disease.

  • Second-line/Refractory Disease: Biologics are highly effective, particularly IL-1 inhibitors (anakinra, canakinumab) and IL-6 inhibitors (tocilizumab).

  • Prognosis: Variable. Some patients have a monocyclic course, others a polycyclic or chronic course. The chronic form is often dominated by destructive arthritis. The life-threatening complication is macrophage activation syndrome (MAS).