Adult-onset Still’s disease (AOSD) refers to a rare inflammatory condition that affects multiple organs and usually presents in young adults. The symptoms typically include fever, rash, and joint pain.

AOSD describes a rare systemic inflammatory condition that affects adults. It is similar to systemic juvenile idiopathic arthritis (SJIA), which is a serious type of juvenile idiopathic arthritis (JIA). However, the distinguishing difference, as the names suggest, is that AOSD occurs in adults, whereas SJIA develops before the age of 16 years. The name derives from Sir George Frederic Still, who discovered the condition.

In this article, we discuss adult-onset Still’s disease in more detail, including its potential causes, symptoms, and treatments.

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AOSD is a rare auto-inflammatory disease that affects the entire body. The cause of the condition is unknown, but it results in characteristic symptoms that include fever, a pink-colored rash, and joint pain. AOSD presents in adulthood, with most cases beginning between 16 and 35 years of age. There are two peaks in the age of onset: 15–25 years and 36–46 years.

Evidence suggests that AOSD has an estimated incidence of 0.14–0.40 cases per 100,000 people and a prevalence of 1–34 cases per 1 million people. Doctors typically diagnose AOSD when certain symptoms develop in adulthood. However, some health experts also use this term to describe individuals with SJIA who have reached adulthood.

The symptoms, course, and severity of AOSD vary from person to person. The condition may appear suddenly and disappear. A person may develop and experience a single episode and then have no symptoms for several years. In other people, the condition persists. The three hallmark symptoms present in 75–95% of those affected are:

  • Fever: A person may experience a fever higher than 39°C that recurs daily and returns to normal between spikes. It often occurs later in the day and precedes other symptoms.
  • Rashes: A visible symptom of AOSD is a pink or salmon-colored maculopapular rash that is not itchy. The rash predominantly appears on the trunk and parts of the limbs near the trunk. Heat or rubbing the skin can induce the rash.
  • Joint pain: Initially, joint pain may be mild and transient, affecting fewer than five joints. Commonly involved joints include the knees, wrists, and ankles. However, it may progress and become severe and destructive, affecting multiple joints, including small ones.

Other common symptoms include:

Meanwhile, less common symptoms may include:

The course of AOSD occurs in three main patterns:

  • Monophasic: This refers to a single episode of symptoms that may last from weeks to months but persists for less than a year.
  • Polyphasic, or intermittent: This describes when a person develops more than one episode of symptoms. The individual may be symptom-free for weeks to years between episodes, and subsequent episodes tend to be shorter and less severe.
  • Chronic: In the chronic form, the symptoms persist over time.

At present, researchers are unsure of the cause of AOSD and refer to the condition as idiopathic. However, they believe that a combination of genetic factors and an infection that acts as a trigger may play a role.

Some evidence suggests that genes that produce proteins to help mediate inflammation likely play a role in the development of the condition. For example, genes such as IL1A and TNFRSF1A provide instructions for making proteins called interleukin-1 alpha and tumor necrosis factor receptor 1, respectively. High activity of these proteins is common in those with AOSD.

Similarly, certain infectious agents may trigger or exacerbate symptoms of AOSD. These may include:

  • Yersinia enterocolitica
  • Mycoplasma pneumoniae
  • cytomegalovirus (CMV)

As such, AOSD may be a reactive condition in which certain infections act as triggers in a genetically predisposed individual.

Currently, research suggests there are no known risk factors, and there is usually no family history. The symptoms typically present before the age of 40 years, and the conditions may be slightly more prevalent in females.

There is no single test to distinguish AOSD from other conditions. A doctor will typically diagnose AOSD through:

  • a comprehensive clinical evaluation and history taking
  • identification of characteristic findings
  • ruling out other possible conditions
  • blood tests and imaging tests

Doctors may use various imaging tests, such as:

  • an X-ray or MRI scan to see organ, bone, and joint damage, including narrowing of the wrist joint space
  • an ultrasound to check for liver or spleen enlargement
  • an echocardiogram to detect inflammation of the pericardium or myocardium of the heart

They may also carry out several blood tests, including:

There are different classification criteria for AOSD, but the Yamaguchi criteria is the most commonly used and has the highest sensitivity. A person will receive a diagnosis if they meet five or more criteria, including at least two of the major criteria.

The major criteria are:

  • having a high fever of at least 39°C for at least 1 week
  • joint pain or arthritis for at least 2 weeks
  • a non-itchy salmon-colored rash on the trunk or limbs
  • an elevated white blood cell count of at least 10,000 cells per microliter

The minor criteria are:

  • a sore throat
  • swollen lymph nodes
  • a swollen liver or spleen
  • unusual liver function test results
  • negative test results for RF and ANA

The aims of treatment are:

  • reducing inflammation
  • controlling symptoms
  • preventing end organ damage

Doctors may prescribe or recommend various medications to treat AOSD. These may include:

A person may still need to take these medications even after the symptoms go away. This maintenance therapy can keep inflammation under control and prevent further bone, cartilage, and organ damage.

People can take steps to help manage the symptoms of AOSD. These steps include:

  • Engaging in regular physical activity: Exercising and staying active can help maintain the range of motion of the joints and keep the muscles strong. It can also help a person maintain a moderate weight, reducing strain on the joints.
  • Adhering to a healthy eating pattern: Alongside exercise, a nutritious, balanced diet can help control a person’s weight, improve energy levels, and reduce fatigue.
  • Reducing strain: Using joint protection techniques, pacing activities carefully, and including sufficient breaks in the day can help reduce the strain on joints.
  • Improving mental well-being: Stress can worsen the symptoms of AOSD. Good sleep hygiene, relaxation techniques, talking therapies, and counseling can all help people manage their mental health.

Adult-onset Still’s disease is a rare autoimmune inflammatory condition characterized by symptoms of fever, joint pain, and salmon-pink rashes. The condition develops in adulthood and is similar to systemic juvenile idiopathic arthritis, which occurs in childhood.

AOSD can have different patterns, meaning that some people only experience a single episode, whereas others have persistent symptoms. Currently, there is no known cause and no set treatment protocol. However, medications, self-care, and lifestyle behaviors can help people manage the condition.

A person should talk with a doctor to identify the best treatment and management plan for their symptoms.