The changes are indistinguishable from those observed in IgA nephropathy. HSP can develop after infections with streptococci (β-haemolytic, Lancefield group A), hepatitis B, herpes simplex virus, parvovirus B19, Coxsackievirus, adenovirus, Helicobacter pylori, measles, mumps, rubella, Mycoplasma and numerous others. Drugs linked to HSP, usually as an idiosyncratic reaction, include the antibiotics vancomycin and cefuroxime, ACE inhibitors enalapril and captopril, anti-inflammatory agent diclofenac, as well as ranitidine and streptokinase. Several diseases have been reported to be associated with HSP, often without a causative link. Only in about 35% of cases can HSP be traced to any of these causes.The exact cause of HSP is unknown, but most of its features are due to the deposition of abnormal antibodies in the wall of blood vessels, leading to vasculitis. These antibodies are of the subclass IgA1 in polymers; it is uncertain whether the main cause is overproduction (in the digestive tract or the bone marrow) or decreased removal of abnormal IgA from the circulation. It is suspected that abnormalities in the IgA1 molecule may provide an explanation for its abnormal behaviour in both HSP and the related condition IgA nephropathy. One of the characteristics of IgA1 (and IgD) is the presence of an 18 amino acid-long "hinge region" between complement-fixating regions 1 and 2. Of the amino acids, half is proline, while the others are mainly serine and threonine. The majority of the serines and the threonines have elaborate sugar chains, connected through oxygen atoms (O-glycosylation).
Obstruction  may refer to:

Places
Obstruction Island, in Washington state
Obstruction Islands, east of New Guinea

Medicine
Obstructive jaundice
Obstructive sleep apnea
Airway obstruction, a respiratory problem
Recurrent airway obstruction
Bowel obstruction, a blockage of the intestines. Gastric outlet obstruction
Distal intestinal obstruction syndrome
Congenital lacrimal duct obstruction
Bladder outlet obstruction

Politics and law
Obstruction of justice, the crime of interfering with law enforcement
Obstructionism, the practice of deliberately delaying or preventing a process or change, especially in politics
Emergency Workers (Obstruction) Act 2006

Science and mathematics
Obstruction set in forbidden graph characterizations, in the study of graph minors in graph theory
Obstruction theory, in mathematics
Propagation path obstruction
Single Vegetative Obstruction Model

Sports
Obstruction (baseball), when a fielder illegally hinders a baserunner
Obstructing the field

See also
The Five Obstructions, a 2003 film
USS Obstructor, an American minelayer ship used in World War II