HSP stands for Henoch-Schönlein purpura, which is a disease that causes small blood vessels to become inflamed and leak. This results in a rash and can affect other organs like the kidneys. HSP is considered a type of vasculitis because it involves inflammation of blood vessels. Vasculitis refers to a group of disorders that cause blood vessel inflammation. So HSP is categorized as a vasculitis since it causes inflammatory damage to small blood vessels.
What is HSP?
HSP is an immunoglobulin A (IgA)-mediated disorder that results in a buildup of IgA antibodies in blood vessel walls. This triggers inflammation that makes the vessels leaky. The exact cause is unknown but often follows an upper respiratory infection.
The primary symptoms of HSP include:
- Palpable purpura – A purplish rash made up of tiny bruises called petechiae. Often appears on legs, buttocks, and elbows. The ankles are often affected.
- Arthralgia – Joint pain.
- Abdominal pain – Stomach pain that can mimic appendicitis or intussusception.
- Gastrointestinal bleeding – May cause bloody diarrhea.
- Kidney inflammation – Can cause hematuria (blood in urine) and proteinuria (protein in urine).
HSP typically affects children, with most cases occurring between ages 2-11 years old. It more commonly affects boys than girls. Symptoms often develop 1-3 weeks after a respiratory infection and then usually resolve within 4-6 weeks as the antibodies clear. However, there is a risk of long-term kidney damage. Treatment focuses on relieving symptoms. Corticosteroids may help reduce severity.
Key features of HSP
There are several key features that help characterize HSP:
- Small vessel leucocytoclastic vasculitis – Inflammation of small blood vessels caused by neutrophil accumulation.
- Immunoglobulin A deposits – IgA antibody deposits found in vessel walls.
- Common skin and kidney involvement – Palpable purpura rash and potential kidney impairment.
- Bowel angina – Abdominal pain with gastrointestinal bleeding.
- Recent upper respiratory infection – Often follows a strep throat or viral illness.
- Mostly affects children – Peak age of onset is 2-11 years old.
- Self-limited course – Symptoms typically resolve in 4-6 weeks.
These signs and symptoms help distinguish HSP from other types of vasculitis and guide appropriate diagnosis.
How does HSP cause vasculitis?
The exact cause of HSP is unknown but it appears to be triggered by an autoimmune reaction. Here is what is believed to occur:
- An upper respiratory infection or other trigger causes increased IgA production.
- These IgA antibodies mistakenly target the body’s own cells and tissues.
- IgA immune complexes build up in small vessel walls, triggering inflammation.
- This leads to leukocytoclastic vasculitis – white blood cells accumulate and cause damage to vessel walls.
- The inflammatory process makes blood vessels leaky.
- Fluid, blood, and proteins leak out into surrounding tissues.
- This results in palpable purpura, joint swelling, abdominal pain, and kidney involvement.
Therefore, HSP is an autoimmune reaction where IgA antibodies mistakenly target the body’s small blood vessels. This leads to vasculitis characterized by vessel inflammation and damage.
Role of streptococcal infection
It is believed strep throat and streptococcal infections play a key role in triggering HSP. The Theory is:
- Strep infection causes increased IgA production.
- Some of these IgA antibodies wrongly react with parts of vascular endothelial cells.
- This leads to immune complex deposition in vessels.
- Subsequent inflammation results in characteristic HSP rash and symptoms.
So while the exact cause remains uncertain, streptococcal infections are likely an important factor in driving the autoimmune response underlying HSP vasculitis.
Is HSP a type of hypersensitivity vasculitis?
Yes, HSP is considered a type of hypersensitivity vasculitis. Hypersensitivity vasculitis is vasculitis triggered by hypersensitivity to an antigen. This results in immune complex deposition in vessel walls.
HSP fits this definition because:
- It appears to involve hypersensitivity to streptococcal antigens.
- Immune complexes form and deposit in vessel walls.
- This causes localized vasculitis when neutrophils are recruited.
Therefore, HSP represents a form of Type 3 hypersensitivity vasculitis driven by immune complex deposition and vessel inflammation. This mechanism classifies it as hypersensitivity vasculitis.
Other types of hypersensitivity vasculitis
Examples of other hypersensitivity vasculitis disorders include:
- Cryoglobulinemic vasculitis
- Serum sickness
- Drug-induced hypersensitivity reactions
- Goodpasture’s syndrome
These involve immune complex formation and vessel inflammation driven by hypersensitivity reactions. HSP shares these key mechanisms.
How is HSP differentiated from other vasculitis syndromes?
HSP has some overlap with features of other vasculitides but also has some distinct characteristics that help differentiate it, including:
IgA-dominant immune complexes
HSP specifically involves IgA-containing immune complex deposition. Other vasculitides are driven by IgG or IgM antibodies.
Lack of ANCAs
HSP lacks antineutrophil cytoplasmic antibodies (ANCAs). These autoantibodies characterize other vasculitides like granulomatosis with polyangiitis.
Small vessel inflammation
HSP affects small vessels like capillaries and venules. Other vasculitides like polyarteritis nodosa cause medium vessel inflammation.
Palpable purpura rash
The characteristic rash with papules and petechiae is unique for HSP. The distribution on the lower limbs and buttocks also helps differentiate it.
Peak age of onset
Occurring predominantly in young children differentiates HSP from conditions like microscopic polyangiitis that more commonly affect adults.
So while HSP has some overlapping features with other vasculitides, the specific clinical and laboratory findings help distinguish HSP as unique among systemic vasculitis syndromes.
What conditions are associated with HSP?
HSP has been associated with several other conditions, including:
Infections
- Upper respiratory infections – Especially streptococcal.
- Hepatitis B and C.
- Mycoplasma pneumonia.
- Group A Strep infections.
- Coxsackievirus.
Infections, particularly with streptococcus bacteria, often precede HSP and may trigger it through autoimmune mechanisms.
Inflammatory disorders
- Inflammatory bowel disease.
- Rheumatoid arthritis.
- Systemic lupus erythematosus.
HSP has been linked to other conditions caused by inflammation and autoimmunity.
Medications
- Penicillins.
- Cephalosporins.
- Vaccinations.
Certain medications have also been reported to trigger HSP in some cases.
Malignancy
- Hematologic cancers like lymphoma and leukemia have very rarely been associated with HSP.
So while infections appear the most likely trigger, HSP has connections with other autoimmune conditions, certain drugs, and rarely even cancers.
What are the complications of HSP vasculitis?
While most HSP cases resolve without issue, there are some potential complications to be aware of:
Kidney involvement
- Hematuria – Blood in the urine, in ~20% of patients.
- Proteinuria – Excess protein in urine, in ~40% of patients.
- Nephrotic syndrome – Protein loss and edema, rare.
- Chronic kidney disease – Progressive loss of function, uncommon.
- End-stage kidney failure – Very rare (~1-3% cases).
Kidney problems like hematuria and proteinuria often resolve but a minority may develop chronic kidney impairment.
Gastrointestinal bleeding or perforation
- Bleeding into the bowel – Can cause bloody diarrhea.
- Bowel wall perforation – Very rare but serious complication.
Intussusception
- Bowel telescoping into itself – More common in young children.
- Causes bowel obstruction requiring reduction.
Encephalopathy
- Rare brain inflammation.
- Ranges from irritability to seizures and coma.
Joint contractures
- Reduced range of motion.
- Due to loss of fluid in the joint space.
So while mostly self-limited, HSP vasculitis can sometimes lead to kidney dysfunction, bowel complications, neurologic issues, and joint problems in severe cases.
What is the long-term outlook for HSP?
The long-term prognosis for HSP is generally good. A few key statistics on the long-term course:
- Complete recovery within 4-6 weeks – ~50-60% of patients
- Recurrences in first 6 months – ~30% frequency
- Chronic kidney disease – Under 5% of pediatric cases
- Progression to end-stage renal failure – 1-3%
- Death from HSP complications – Extremely rare
So while recurrences affect a minority and chronic kidney dysfunction can occur, overall HSP has a good long-term prognosis with low mortality. However, follow-up is vital to monitor for rare but serious complications.
Conclusion
In summary, HSP represents a type of leukocytoclastic vasculitis affecting small vessels and characterized by IgA-dominant immune complex deposition. Key features include palpable purpura rash, arthralgia, bowel angina, and potential kidney involvement. HSP is considered a form of hypersensitivity vasculitis driven by autoimmune-mediated inflammation. While mostly self-limited, complications like chronic kidney disease can occasionally occur. Overall, HSP generally carries a good long-term prognosis. Recognizing HSP as a distinct form of primary systemic vasculitis is key for guiding management.