Cases of hives often go undiagnosed as to the cause, but hives and swollen joints in combination should lead you to investigate the possibility of Serum sickness as a cause. Serum sickness is not a well known response but could explain hives and swollen joints occurring at the same time. While a number of other allergic reactions could also explain the hives, swollen joints is kind of a wild card that can help you narrow it down.

What is Serum Sickness?

Serum sickness is an allergic-like reaction to injected proteins used to treat immune conditions. The injected proteins, or antiserum, are the liquid part of the blood that has antibodies in it to help protect against infections or even poisons.

The clear fluid portion of the blood is called plasma. It doesn’t contain any blood cells, but does contain proteins including antibodies. Antiserum is produced from this plasma and there are many types of antiserums produced for different reasons. Well known antiserum injections are those given for exposure to tetanus and rabies. But that is far from a complete list.

Serum sickness is defined as a false immune system response to the proteins in this plasma. The immune system attacks the antiserum and causes hives and swollen joints, inflammation, and other symptoms. The immune system is indeed a complex and marvelous system but when it goes “rogue” it can cause real problems – some severe. In essence, it attacks the body from within.

Can Other Types of Medication Cause Serum Sickness?

Some medications can cause similar reactions, like fever, rash, hives, and swollen joints.  But it is not exactly the same. These medications will trigger a response in fairly short order.  On the other hand, serum sickness usually develops one to three weeks after the first injection. Medications that mimic serum sickness symptoms include penicillin, cefaclor, and sulfa.

Some injected proteins like antithymocyte globulin and rituximab which are used to combat transplant rejection and immune disorders can also cause the hives and swollen joints associated with serum sickness.

Finally, some blood products can cause serum sickness as well.

How is it Diagnosed?

Diagnosis will depend mostly on seeing blood and proteins in the urine and immune complexes in the blood. Blood vessel inflammation and enlarged lymph nodes are also common.