Jarisch-Herxheimer reaction

Jarisch-Herxheimer reaction (JHR) is a febrile reaction often accompanied by headache, myalgia (muscle pain), and an exacerbation of skin lesions that occurs after the initiation of antibiotics in certain bacterial infections. It is most commonly observed in the treatment of syphilis, Lyme disease, and relapsing fever. The reaction is believed to be caused by the release of endotoxin-like substances or cytokines from the killed or dying bacteria.

Causes and Mechanism

The Jarisch-Herxheimer reaction is primarily associated with the treatment of syphilis, caused by the bacterium Treponema pallidum, and Lyme disease, caused by Borrelia burgdorferi. It can also occur during the treatment of relapsing fever, which is caused by various species of Borrelia. The reaction occurs when large quantities of toxins are released into the body as bacteria die off during antibiotic treatment. The sudden influx of toxins overwhelms the body's ability to clear them, leading to a febrile reaction characterized by fever, chills, and malaise.

Symptoms

Symptoms of the Jarisch-Herxheimer reaction typically begin within a few hours of the first dose of antibiotics and can include:

• Fever
• Chills
• Headache
• Myalgia (muscle pain)
• Hypotension (low blood pressure)
• Tachycardia (rapid heart rate)
• Exacerbation of existing skin lesions

Diagnosis

Diagnosis of the Jarisch-Herxheimer reaction is primarily clinical, based on the temporal relationship between the onset of symptoms and the initiation of antibiotic therapy in a patient being treated for a known spirochetal infection. There are no specific laboratory tests to confirm the reaction.

Treatment

Treatment of the Jarisch-Herxheimer reaction is supportive and symptomatic. Measures may include:

• Administration of antipyretics (fever-reducing medications) such as acetaminophen or ibuprofen
• Adequate hydration
• Monitoring and support of cardiovascular and respiratory function in severe cases

Prevention of the reaction can sometimes be achieved by starting with lower doses of antibiotics and gradually increasing to the full dose, although this approach is not always effective.

Prognosis

The Jarisch-Herxheimer reaction is generally self-limiting and resolves within 24 to 72 hours. While it can be alarming, especially in cases with severe symptoms, it does not typically indicate a need to stop or change antibiotic therapy.

Epidemiology

The incidence of the Jarisch-Herxheimer reaction varies depending on the disease being treated and the specific population. It is more commonly reported in the treatment of early syphilis and less frequently in late syphilis or Lyme disease.