Macroamylasemia attributable to gluten-related amylase autoantibodies: A case report

Background. Macroamylasemia (MA) is a benign condition caused by circulatin g macroamylase complexes of pancreatic or salivary amylase bound to plasma proteins, which cannot be cleared by the renal glomeruli. In most cases, th e macromolecular amylase represents a complex of normal amylase and either immunoglobulin A or G and may be a specific antigen-antibody complex. Celia c disease (CD) is a permanent intolerance to ingested gluten that results i n immunologically mediated inflammatory damage of the small intestinal muco sa. Several recent population-based serologic surveys have shown CD to be a common disorder, possibly affecting 1 in 200 to 250 individuals in most co untries studied, including the United States, where overt CD is rare, indic ating a high proportion of subclinical disease. The diagnosis of CD current ly rests on the histological demonstration of the characteristic lesion in the small intestine and the subsequent clinical response to the introductio n of a gluten-free diet. MA associated with CD has been described in adult patients, and in a few cases, MA decreased or resolved after a strict glute n-free diet. A few single cases of MA have been described in childhood, but no association with CD has been reported so far. We report a girl with CD, autoimmune thyroiditis, and MA, in whom CD-related antibodies to amylase a nd to exocrine pancreas tissue resolved with a gluten-free diet. Case Report. An 11-year-old girl was referred for chronic abdominal pain an d growth retardation associated with persistent hyperamylasemia and suspect ed chronic pancreatitis. We confirmed elevated serum amylase, normal serum lipase, and very low 24-hour urine amylase and amylase clearance/creatinine clearance ratio, consistent with MA. Serologic tests for CD were positive, and the diagnosis was confirmed by small bowel biopsy showing subtotal vil lous atrophy. Thyroid function tests showed a pronounced hypothyroidism, as sociated with high titers of thyroid microsomal and thyroglobulin antibodie s. Screening for other autoantibodies-including antinuclear, islet cell, gl utamic acid decarboxylase, protein tyrosine phosphatase islet antigen 512, adrenal gland, and cytoplasmic neutrophil granulocyte antibodies-was negati ve. A diagnosis of CD, MA, and hypothyroidism attributable to autoimmune th yroiditis was made. A gluten-free diet and oral replacement with L-thyroxin e was started with clinical improvement. Serum amylase and amylase clearanc e/creatinine clearance ratio normalized, consistent with resolution of MA. Study Design and Methods. The patient's serum samples were obtained at the time of CD diagnosis and at 3 and 12 months after instituting a gluten-free diet. Serum samples from 10 consecutive untreated celiac children were dis ease controls, and 39 participants with no gastrointestinal symptoms and no family history of CD served as healthy controls. The origin of MA as deter mined by complexes of amylase with circulating immunoglobulins was tested b y the measurement of amylase on supernatants after precipitation of immune complexes with either protein A Sepharose or polyethylene glycol. The preci pitation of >60% of amylase activity was consistent with the presence of MA . Immunoglobulin G (IgG) and immunoglobulin A (IgA) circulating autoantibod ies to amylase were measured using recently developed enzyme-linked immunos orbent assay (ELISA), using porcine amylase as antigen. Results were expres sed as arbitrary units (AUs). Statistical analysis was performed by Student 's t test for unpaired data. IgA and IgG antibodies to exocrine pancreas ti ssue were detected by indirect immunofluorescence on human pancreas cryosec tions. Results. Serum immunoprecipitation with either protein A Sepharose or polye thylene glycol reduced amylase activity from 1698 to 89 U/L (94.8%) and to 75 U/L (95.6%), with only marginal reduction in control serum samples. The ELISA for autoantibodies to amylase detected high values, both IgA (3531 AU ) and IgG (1855 AU), in the serum sample from the patient at CD diagnosis. IgA autoantibodies (mean +/- standard deviation) were 3.4 +/- 2.5 AU in hea lthy controls, and 2.1 +/- 1.2 AU in celiac controls; IgG autoantibodies we re 10 +/- 4.8 AU in healthy controls and 8.5 +/- 3.2 AU, respectively. Auto antibodies to exocrine pancreas tissue were documented in patient sera at t he time of CD diagnosis, both IgA and IgG, but not in control groups. Prein cubation of patient's serum with excess of alpha -amylase specifically inhi bited antibody binding to coated amylase in the ELISA, and partially inhibi ted immunoreactivity to exocrine pancreas. Autoantibodies to alpha -amylase and to exocrine pancreas declined in CD patients after institution of a gl uten-free diet. Conclusions. Few cases of MA have been described in children, and in all am ylase determination was part of the clinical investigation for abdominal pa in or trauma. We describe the first pediatric case report of MA associated with CD and autoimmune thyroiditis. The association of autoimmunity to exoc rine pancreas tissue with CD is intriguing. CD is frequently found in assoc iation with pancreatic islet cell autoimmunity and with clinical type 1 dia betes. In our case, endocrine pancreas seemed to be spared by the autoimmun e process, because we could not demonstrate islet cell and islet-specific a utoantibodies. A relationship of pancreatic autoimmunity and CD is suggeste d by the parallel decline and disappearance of both CD and pancreas autoant ibodies after gluten withdrawal. These finding are consistent with the incr easing recognition of autoantibodies as a manifestation of CD and regressio n of these antibodies with treatment of a gluten-free diet. The mechanisms underlying the formation of MA in CD and the site of production of amylase- binding antibodies have been poorly defined and can only be hypothesized. I t is possible that at the intestinal level, crossreactivity either with glu ten-related or other antigens occurs, resulting in autoantibody formation t o pancreas serum amylase. Nevertheless, our findings suggest a correlation between CD and MA, because it resolved with institution of a gluten-free di et. Because CD may be silent and undiagnosed, we suggest screening for the disease in patients with MA.