HIGH-SENSITIVITY DIAGNOSIS OF AA AMYLOIDOSIS USING CONGO RED AND IMMUNOHISTOCHEMISTRY DETECTS MISSED AMYLOID DEPOSITS

Biopsy diagnosis of early amyloid-A (AA) amyloidosis has often been di fficult. Examination of 57 consecutive biopsy specimens from 42 patien ts with inflammatory pediatric diseases permitted comparison of the pr ecision of biopsy amyloid diagnosis in six different laboratories (lab s), which applied the following methods: Congo red alone (four unspeci alized labs combined as Lab 1), Congo red and electron microscopy (Lab 2), or Congo red and immunohistochemistry using monoclonal antibodies (Lab 3). Lab 3 reexamined the diagnoses made by Lab 1 and Lab 2. Of t he 42 patients, 17 patients with 32 biopsies were selected for this st udy based on the presence of amyloid in at least one biopsy. Whereas m assive or no amyloid was concordantly recognized by all labs in 18 bio psies from nine patients, discordance was demonstrated in 14 biopsies from eight patients. Comparison of Labs 1-3 revealed amyloid in 12 rec tal and 18 renal biopsies evaluated by Lab 3, whereas Lab 2 missed amy loid in two of 18 renal biopsies and Lab 1 missed amyloid in 11 of 12 rectal biopsies, Most amyloid was missed when only minute amounts of a myloid were present. Had out technique (Lab 3) been available at the t ime of biopsy, amyloid could have been diagnosed years earlier, thereb y sparing the patient further biopsies and allowing initiation of earl ier treatment before organ damage could occur.