HSP has some very different symptoms, swelling, arthritis and rash.
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Who would think these things came together? It is the rash which makes diagnosis definite. However it is not the usual type of rash. It is sort of a cross between a rash an bruising. It is caused by the capillaries leaking. The illness usually effects children. It is more common in boys than girls. Adult onset of the illness can be much more severe.
It is relatively rare, and even though doctors know of this ailment, treatments a pretty much non existent other than to treat for pain. there are some things to keep an eye on with this condition. These are the kidneys and the intestines. If the ailment effects these areas then it can cause long terms effects.
All symptoms seem to be caused by a weakening of the capillaries. Although the cause of the ailment is not known, the best guess is that the body's immune system is over stimulated (as a reaction to an infection or a medication) and begins to attack the body. It takes a while for the body to turn this off, 2-6 weeks. It usually goes away. However it can come back with other bouts, but usually not as severe.