Serum Sickness
Overview
Serum sickness is a type of hypersensitivity reaction that occurs when the immune system reacts to certain proteins in antiserum, a serum containing antibodies. This condition is classified as a type III hypersensitivity reaction, which involves immune complex-mediated mechanisms. Serum sickness can result from the administration of antiserum derived from animal sources, such as horse or rabbit, used in the treatment of various conditions, including snake bites, rabies, and diphtheria.
Pathophysiology
Serum sickness occurs when the immune system generates an immune response against foreign proteins introduced into the body. The formation of immune complexes, consisting of antigens and antibodies, is central to the pathogenesis of serum sickness. These immune complexes circulate in the bloodstream and can deposit in various tissues, leading to inflammation and tissue damage.
The immune complexes activate the complement system, a group of proteins that play a crucial role in immune responses. Activation of the complement system leads to the recruitment of inflammatory cells, such as neutrophils and macrophages, to the sites where immune complexes have deposited. This results in the release of inflammatory mediators, including cytokines and chemokines, which contribute to the clinical manifestations of serum sickness.
Clinical Manifestations
The symptoms of serum sickness typically develop 7 to 14 days after exposure to the offending antigen. Common clinical manifestations include:
- **Fever**: Elevated body temperature is often one of the first signs of serum sickness.
- **Rash**: A widespread, erythematous rash may appear, often accompanied by itching.
- **Arthralgia**: Joint pain and swelling are common, particularly in the knees, wrists, and ankles.
- **Lymphadenopathy**: Enlargement of lymph nodes can occur, particularly in the cervical and axillary regions.
- **Urticaria**: Hives or welts may develop on the skin.
- **Angioedema**: Swelling of the deeper layers of the skin, often around the eyes and lips.
In severe cases, serum sickness can lead to complications such as nephritis, myocarditis, and vasculitis.
Diagnosis
The diagnosis of serum sickness is primarily clinical, based on the characteristic symptoms and a history of exposure to antiserum or other foreign proteins. Laboratory tests may support the diagnosis and include:
- **Complete Blood Count (CBC)**: May show leukocytosis or leukopenia.
- **Erythrocyte Sedimentation Rate (ESR)**: Elevated ESR indicates inflammation.
- **C-Reactive Protein (CRP)**: Increased CRP levels are a marker of inflammation.
- **Complement Levels**: Reduced levels of complement components (C3 and C4) may be observed due to their consumption in immune complex formation.
- **Urinalysis**: May reveal proteinuria or hematuria if renal involvement is present.
Treatment
The management of serum sickness involves the removal of the offending antigen and symptomatic treatment. Key therapeutic approaches include:
- **Discontinuation of the offending agent**: If the serum sickness is due to a specific antiserum, its administration should be stopped immediately.
- **Corticosteroids**: These are often used to reduce inflammation and alleviate symptoms. Prednisone is commonly prescribed.
- **Antihistamines**: These can help control itching and urticaria.
- **Analgesics and Antipyretics**: Medications such as acetaminophen or nonsteroidal anti-inflammatory drugs (NSAIDs) can be used to manage pain and fever.
- **Plasmapheresis**: In severe cases, plasmapheresis may be considered to remove circulating immune complexes from the bloodstream.
Prognosis
The prognosis for serum sickness is generally favorable, with most patients experiencing complete resolution of symptoms within a few weeks after discontinuation of the offending agent and appropriate treatment. However, severe cases with complications may require more intensive management and have a more prolonged course.
Prevention
Preventive measures for serum sickness include:
- **Use of Human-Derived Antibodies**: Whenever possible, human-derived antibodies or monoclonal antibodies should be used instead of animal-derived antisera to reduce the risk of serum sickness.
- **Pre-Treatment Testing**: Skin testing for hypersensitivity reactions may be performed before administering antiserum.
- **Patient Education**: Patients should be informed about the potential risks of serum sickness and advised to report any symptoms promptly.