Commentary by

Tan, Heng Soon MD, Brigham and Women's Primary Care Associates at Newton Corner, Harvard Medical School, Boston, MA, USA on Jan 24, 2006

Clinically she has Henoch Schonlein purpura that is frequently associated with asymptomatic microhematuria. Diagnosis is made on skin biopsy that shows small vessel vasculitis consistent with leucocytoclastic vasculitis. IgA deposits can be found in both skin and renal biopsy. Though vasculitis may be recurrent, no treatment is necessary since the prognosis is good with spontaneous recovery and no long term sequelae.

IgA nephropathy is at risk for progression only in presence of increasing proteinuria and later development of impaired renal function and hypertension. The presence of asymptomatic strep pharyngitis raises the possibility of poststrep glomerulonephritis to explain microhematuria, however, this is not consistent with recurrent vasculitis. So her clinical presentation is best explained by Henoch Schonlein purpura.

I enclose relevant paragraphs from Up To Date and PubMed that provide more discussion:

Henoch-Schönlein purpura (HSP) is characterized by the tissue deposition of IgA-containing immune complexes [1]. The pathogenesis of this disorder may be similar to that of IgA nephropathy, which is associated with identical histologic findings in the kidney. (See "Causes and diagnosis of IgA nephropathy"). The observation of the simultaneous occurrence of HSP and IgA nephropathy in twins after an adenovirus infection is further evidence in support of a common pathogenesis [2].
IgA deposition is prominent in both HSP and IgA nephropathy, but the renal injury may be mediated at least in part by IgG autoantibodies directed against mesangial cell antigens [3,4]. The course of the renal disease and circulating antibody titers are roughly parallel, and these autoantibodies do not appear to be present in those patients with HSP who do not have renal involvement [4].

Confirmation of the diagnosis of HSP requires evidence of tissue deposition in the skin or kidney of IgA by immunofluorescence microscopy (show histology 1). Biopsy of the skin lesions reveals inflammation of the small blood vessels, called a leukocytoclastic vasculitis, that is most prominent in the postcapillary venules (show histology 2A-2B). This finding is relatively nonspecific (also being found in other forms of hypersensitivity vasculitis) unless accompanied by vascular IgA deposition which can, in some cases, also be seen in areas of seemingly uninvolved skin [34]. Renal biopsy is another method to establish the diagnosis, but this invasive procedure is generally reserved for patients in whom the diagnosis is uncertain or in whom there is clinical evidence of more severe renal involvement.

There are three major causes of glomerular hematuria after a URI: IgA nephropathy; poststreptococcal glomerulonephritis; and a nonspecific mesangioproliferative glomerulonephritis.
IgA NEPHROPATHY — IgA nephropathy is probably the most common cause of glomerulonephritis [3,4]. (See "Causes and diagnosis of IgA nephropathy"). Patients with this disorder often have recurrent episodes of gross hematuria, beginning 1 to 3 days after a URI. The urine color typically returns to normal within a few days, although microscopic hematuria may persist indefinitely in patients with chronic disease.
The glomerular filtration rate is generally normal or only mildly reduced during the acute episodes. However, acute renal failure that is usually reversible can occur in patients with gross hematuria [8]. (See "Treatment and prognosis of IgA nephropathy", section on Acute renal failure with gross hematuria).
POSTSTREPTOCOCCAL GLOMERULONEPHRITIS — Poststreptococcal glomerulonephritis is induced by infection with specific nephritogenic strains of group A, ß-hemolytic streptococci (such as type 12 and type 49) [9-12]. A current leading candidate for the causative antigen is nephritis-associated streptococcal antigen [13,14]. The antigen has been identified as a plasminogen receptor, which can activate the alternate complement pathway.
Poststreptococcal glomerulonephritis can occur in sporadic cases or during an epidemic. The incidence of clinically detectable glomerulonephritis in children infected during an epidemic is about 5 to 10 percent with pharyngitis and 25 percent with skin infections [9,10]. Younger children below the age of seven appear to be at highest risk.
The clinical presentation can vary from asymptomatic, microscopic hematuria to the full-blown acute nephritic syndrome, characterized by red to brown urine, proteinuria (which can reach the nephrotic range), edema, hypertension, and acute renal failure [2,5,11].
Although the presentation may be similar to that seen with IgA nephropathy, the following can be used to differentiate between these disorders. Renal biopsy is not required in most cases.
The latent period from infection to hematuria in poststreptococcal glomerulonephritis averages 10 days with pharyngitis (and 21 days with impetigo) versus less than 5 days in IgA nephropathy [11].

Recurrent episodes of gross hematuria are common in IgA nephropathy but rare in poststreptococcal glomerulonephritis, perhpas because only certain streptococcal strains can cause renal disease (such as M protein type 12 with a URI and type 49 with impetigo) [9,10]. Alternatively, the rarity of second-episodes may be the result of the long-term persistance of antibodies against nephritis-associated streptococcal antigen, a leading candidate for a causative antigen [13,14].

Throat culture and serologic tests (including hypocomplementemia) should be positive in poststreptococcal glomerulonephritis following a URI. This does not necessarily apply to patients with impetigo, only 50 percent of whom have an elevation in antistreptolysin O titers [11]. Inactivation of this antigen by skin lipids may be responsible for this finding. Thus, measurement of other antistreptococcal antibodies, such as anti-DNAase B, or antihyaluronidase [15].

Poststreptococcal glomerulonephritis gradually resolves after the infection has cleared, with renal function beginning to improve within 1 to 2 weeks, complement levels normalizing within 6 weeks, and the hematuria disappearing within 6 months [5,16]. In comparison, persistent microscopic hematuria is common in IgA nephropathy and persistent hypocomplementemia is suggestive of membranoproliferative glomerulonephritis [17].

ETIOLOGY — Most cases of IgA nephropathy are idiopathic. A variety of additional disorders have been associated with IgA nephropathy, Cirrhosis and other forms of severe liver Gluten enteropathy Minimal change disease and membranous nephropathy HIV infection Wegener's granulomatosis Familial disease Bacterial infections include Staphylococcus aureas, Haemophilus parainfluenzae.
Other — IgA nephropathy has also been infrequently associated with a variety of other diseases including dermatitis herpetiformis, seronegative arthritis (particularly ankylosing spondylitis), small cell carcinoma, disseminated tuberculosis, bronchiolitis obliterans, and mycosis fungoides. A common association with cytomegalovirus has also been proposed, but not confirmed by more sensitive techniques.

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