Serum sickness is an immune system, allergy-like reaction to injected animal proteins in antiserum or other medications used to treat immune conditions. Serum sickness-like reactions are similar to serum sickness reactions, but they are to certain non-protein drugs.
While serum is the clear part of blood that does not contain blood cells, it contains proteins, including antibodies, which respond to potentially harmful substances (antigens) such as viruses, bacteria, and parasites that may invade the body. Antiserum is human or animal serum that has been exposed to a certain antigen or antigens, thereby developing particular antibodies. The antiserum may then be used to protect someone who has not been immunized against these antigen(s).
Serum sickness occurs when the immune system misidentifies a protein in the antiserum as an antigen. As a result, the immune system attacks the antiserum. Other drug allergies occur shortly after their second use. Serum sickness, on the other hand, develops approximately one to three weeks after the first exposure to the agent. Symptoms may include:
- Myocardial and pericardial inflammation
- Cutaneous (skin) symptoms including urticaria (hives), scarlatiniform rash (resembling scarlet fever), purpuric or maculopapular lesions, erythema multiforme
- Edema (swelling due to excessive accumulation of fluid), especially about the neck and face
- Joint pain
Arthritis or arthralgias
- Swollen lymph nodes (lymphadenopathy)
- Dyspnea (shortness of breath) and cyanosis (bluish skin due to lack of oxygen)
- Neurologic symptoms/conditions including peripheral neuropathy, optic neuritis (inflammation of nerves), brachial plexus neuritis, cranial nerve palsies, encephalomyelitis (inflammation of the brain and spinal cord), Guillain-Barr syndrome (temporary inflammation of the nerves)
- Renal manifestations (rarely)
- Anaphylactic shock (on subsequent exposures to the same antigen)
Due in part to public health vaccination programs, the need for specific serum antitoxins has decreased, and much of that which continues to be used is refined of its antigenic components to serum sickness. And while blood products and injected proteins such as rituximab (Rituxan), which is used to treat cancers and immune disorders, and antithymocyte globulin (rabbit, Thymoglobulin), which used to treat transplant rejection, continue to cause serum sickness, non-protein drugs are now the most common cause of serum sickness-like reactions.
Drugs that have been implicated include:
Other possible causes of serum sickness include:
- Heterologous serum – blood plasma with the anticoagulant proteins removed. It can also be made synthetically, and is used to teat or protect against botulism, gas gangrene, diphtheria, organ transplant rejection, and spider and snake bites
- Allergen extracts
- Hymenopteran venom – venom from the hymenopteran order of insects, which include bees, wasps, sawflies and ants
- Infectious agents
In addition to the symptoms described, a blood test may reveal blood vessel inflammation and a urine test may show protein in the urine. The urine may also contain blood and the lymph nodes may be tender to the touch. Symptoms may occur more rapidly (approximately 1-4 days after exposure) with subsequent exposures to the same antigen.
Use of the causative agent or antigen should be discontinued. Medications may include:
- Antihistamines – to relieve itching and shorten the course of the illness
- Corticosteroids – ointments or creams to relieve itching; oral corticosteroids such as prednisone for severe cases
- Nonsteroidal anti-inflammatory drugs (NSAIDs) – such as ibuprofen or naproxen to relieve joint pain
Most cases resolve spontaneously although minor symptoms may persist for weeks.