Diagnostic Value of Minor Salivary Glands Biopsy in Systemic Amyloidosis

Amyloidosis is a potentially fatal condition characterized by deposition of extracellular protein in an abnormal fibrillary form with a β-sheet structure, named amyloid, in several organs, especially in heart, kidney and liver. The tissue biopsy, stained with Congo red and demonstrating amyloid deposits with apple-green birefringence, is required for diagnosis. The biopsy of visceral organs is characterized by higher sensitivity although it requires invasive procedures bearing higher risk of complications, such as bleeding, hematoma and perforation. Therefore, fine-needle abdominal fat aspiration is the most common biopsy site. More recently an additional procedure has been performed and is at this time is under evaluation, being represented by minor salivary labial glands biopsy (MSGB) which is characterized by easy accessibility, low complication rate, and lower costs. Reliability of this procedure is under evaluation. We have analyzed all patients referred at our institution between March 2006 and April 2015, with the clinical or laboratory symptoms suggestive for amyloidosis (proteinuria, renal impairment, neuropathy and restrictive cardiomyopathy). In the first three years we performed biopsy by abdominal fat aspiration as first diagnostic step. Patients failing to obtain diagnostic material underwent a second biopsy, including surgical approaches. In order to minimize the use of invasive procedures, we have introduced MSGB, obtained by a small incision inside the lower lip. The sample was then collected and fixed in formalin, stained with Congo red and analyzed by polarized light microscopy. Immunohistochemical examination was performed whenever indicated to discriminate AA and AL amyloidosis.

In our retrospective study we have examined results of MSGB from 44 patients during the time period between January 2008 and April 2015. All patient were affected with AL amyloidosis and 51% of them was associated with multiple myeloma. The deposits were characterized as AL λ in 80% of the patients and AL κ in 20%. The median age was 65 years (range 26-97), 30% were female and 70% male. In 38 patients (86%) the MSGB was positive, while in six (14%) was negative. Of these six patients, two presented localized amyloidosis (diagnosed by tongue and conjunctiva biopsy) and four underwent visceral organ biopsy (3 renal biopsies, 1 myocardial).

MSGB is therefore a simple, safe, and reliable tool for the diagnosis of systemic amyloidosis. The advantages of MSGB include avoidance of more invasive methods, need for a small incision, quite a low risk of bleeding and nerve damage, applicability in the outpatient setting and rapid healing.

In our experience, it was performed in all cases without adverse effects, demonstrating an overall diagnostic sensitivity of 86%. For this reason we introduce this procedure in our clinical practice.