Research Article: Amalgam tattoo versus melanocytic neoplasm – Differential diagnosis of dark pigmented oral mucosa lesions using infrared spectroscopy

Date Published: November 6, 2018

Publisher: Public Library of Science

Author(s): Johannes Laimer, Raphael Henn, Tom Helten, Susanne Sprung, Bettina Zelger, Bernhard Zelger, René Steiner, Dagmar Schnabl, Vincent Offermanns, Emanuel Bruckmoser, Christian W. Huck, Hasan Ayaz.


Dark pigmented lesions of the oral mucosa can represent a major diagnostic challenge. A biopsy is usually required to determine the nature of such intraoral discolorations. This study investigates the potential use of infrared spectroscopy for differential diagnosis of amalgam tattoos versus benign or malignant melanocytic neoplasms.

For this retrospective study, formalin-fixed paraffin-embedded tissue (FFPE) specimens of dark pigmented lesions concerning the oral mucosa or the lip were investigated using mid infrared spectroscopy. The samples were chosen from patients who had undergone a mucosal biopsy at the University Hospital Innsbruck (Austria) between the years 2000 and 2017. Principal component analysis was used for data exploration. Evaluation was based on the superimposition of the recorded spectra and the corresponding histologic slides.

In total, 22 FFPE specimens were analyzed. Clear differences were found between amalgam and non-amalgam samples. A general weakening of the penetrating infrared radiation allowed for unspecific discrimination between these two classes. An overall accuracy in predicting the correct class of 95.24% was achieved.

Infrared spectroscopy appears to be a suitable technique to differentiate between amalgam tattoos and melanocytic lesions in FFPE samples. It could potentially be applied in vivo, too, serving as a non-invasive diagnostic tool for intraoral dark pigmented lesions.

Partial Text

Pigmented lesions of the oral mucosa are a common finding[1]. Exogenous factors like amalgam tattoos represent a major part of these lesions[1]. Most amalgam tattoos are due to dental treatments when metal particles accidentally deposit in open oral wounds or are dashed like a shrapnel into the oral mucosa during tooth preparation procedures[2]. Further, a galvanic element can form if various metals are used as dental restorative material[3]. Thereby, the ignoble metal dissolves and precipitates as an inorganic salt in the oral mucosa. Due to the lymphatic transport of metallic material, the discoloration can increase in size giving the impression of a growing malignant neoplasm[4]. Only in presence of a clear medical/dental history, a dark pigmented lesion can be assumed to be no more than a harmless amalgam tattoo. Bearing in mind that any dark pigmented lesion could not only be a benign discoloration but could potentially represent a melanoma[4–6], a mucosal biopsy for definitive histological diagnosis is usually required[5, 7, 8].

Clinical details regarding the histologically confirmed number of amalgam tattoos as well as the number of both benign and malignant melanocytic lesions can be found in Table 1.

The goal of this study was to evaluate the use of FTIR (Fourier Transform Infrared) spectroscopy to distinguish between intraoral amalgam tattoos (intramucosal metallic foreign bodies) and melanocytic lesions of the oral mucosa.