IgA Vasculitis

An immune complex mediated small vessel vasculitis characterised by deposition of IgA dominant immune complexes in the walls of small vessels, classically producing the tetrad of palpable purpura, arthritis, abdominal pain and renal involvement, occurring predominantly in children but also affecting adults, in whom the disease tends to be more severe with a higher risk of significant renal involvement.

Pathophysiology

Abnormal glycosylation of IgA1 leads to immune complex formation and deposition in the walls of small vessels and the glomerular mesangium, triggering complement activation and vasculitic inflammation. A preceding upper respiratory tract infection is a recognised trigger in a substantial proportion of paediatric cases.

Palpable purpura, typically distributed over the lower limbs and buttocks, symmetrical and appearing in crops, is the hallmark and usually the presenting feature.

Arthritis or arthralgia, typically affecting the knees and ankles, is transient and non erosive, occurring in the majority of cases.

Abdominal pain, colicky in nature, occurs from bowel wall oedema and haemorrhage, and can be severe enough to mimic an acute abdomen, with intussusception a recognised and important complication, particularly in children, requiring prompt recognition.

Renal involvement, ranging from isolated microscopic haematuria to nephrotic or nephritic syndrome and, in a minority, progression to chronic kidney disease, is the principal determinant of long term prognosis and is more frequent and severe in adult onset disease.

Scrotal involvement in boys can mimic testicular torsion and requires careful clinical assessment to avoid unnecessary surgical exploration.

Diagnosis is predominantly clinical, based on the characteristic purpuric rash distribution together with at least one of arthritis, abdominal pain, renal involvement or characteristic histology, particularly in a child with a typical presentation where biopsy is often unnecessary.

Skin biopsy, where performed, shows leukocytoclastic vasculitis with IgA dominant immune deposits on immunofluorescence.

Renal biopsy is indicated for significant or persistent renal involvement (nephrotic range proteinuria, renal impairment, or nephritic features), showing mesangial IgA deposition indistinguishable from IgA nephropathy, and providing important prognostic and treatment guiding information.

Urinalysis and renal function should be checked at diagnosis and monitored regularly for at least six months given the potential for renal involvement to develop or evolve after the initial presentation.

Abdominal ultrasound is warranted for significant abdominal pain given the risk of intussusception, and platelet count and coagulation screen help exclude alternative causes of purpura.

Management is predominantly supportive for the majority of cases, with rest, hydration and simple analgesia (paracetamol, with nonsteroidal anti inflammatory drugs used cautiously given renal involvement risk and avoided with significant renal impairment or gastrointestinal bleeding).

Corticosteroids may reduce the severity and duration of abdominal and joint symptoms, though do not appear to alter the overall disease course or prevent renal involvement, and are generally reserved for significant abdominal pain, severe arthritis or in some protocols for early significant renal disease.

Significant renal involvement, particularly nephrotic syndrome, nephritic features or biopsy proven crescentic change, is managed with corticosteroids and, for more severe disease, additional immunosuppression (mycophenolate mofetil, azathioprine or cyclophosphamide), following principles similar to IgA nephropathy management.

Intussusception, where suspected or confirmed, requires urgent surgical or radiological assessment and management.

The majority of cases, particularly in children, resolve spontaneously within four to six weeks without long term sequelae, though recurrence occurs in a meaningful minority, and long term renal follow up is warranted given the potential for renal involvement to become apparent or progress over subsequent months, with adult patients requiring closer and more prolonged renal surveillance given their higher risk of significant chronic kidney disease.