Other Ways to Identify New Kids on the Block

To the Editor.—We read with interest the well-illustrated review article by Karamchandani et al,¹  “New Kids on the Block: A Review of the Latest Iatrogenic Foreign Materials Seen in Gastrointestinal Specimens,” recently published in Archives of Pathology & Laboratory Medicine. The review provides valuable information and is intended to assist pathologists in recognizing “foreign”/exogenous materials in gastrointestinal specimens, primarily using light microscopy and histochemistry. We agree that “if the relevant clinical history is lacking,”¹  which is unfortunately often the case, identification of these materials can pose diagnostic difficulties.

We would like to add our observations on some of the materials mentioned in the review, and to promote the use of 2 ancillary techniques, scanning electron microscopy with energy-dispersive x-ray analysis and Fourier transform infrared spectroscopy, which, respectively, provide valuable elemental and molecular information for the identification of exogenous materials in tissue. Although these techniques may not be directly available to most pathologists, they are obtainable in referral centers and can be performed on routinely processed, formalin-fixed, paraffin-embedded tissue. Although many diagnostic difficulties associated with the identification of exogenous materials in tissue can be resolved with light microscopy and clinical history, these additional techniques have been useful, in selected cases, over the past several decades.

Scanning electron microscopy with energy-dispersive x-ray analysis was referenced in the discussion of lanthanum carbonate, but the illustration labeled “Electron microscopy identifies irregular electron-dense deposits” (Figure 6, F, in Karamchandani et al¹) appears to be a transmission electron microscopic image (no scale is provided). We provide a scanning electron microscopy image and energy-dispersive x-ray analysis maps for lanthanum, phosphorus, oxygen, and carbon, which confirm the presence and distribution of lanthanum phosphate in a gastric specimen (Figure 1, A through E). In addition, lanthanum phosphate deposits are refractile, a characteristic that is enhanced under dark-field illumination (Figure 2, A and B).

In discussing the differential diagnosis of lanthanum carbonate administration, the authors reference clofazimine. This medication is used for the treatment of a variety of mycobacterial infections other than Mycobacterium leprae infection.^2,3  Clofazimine crystals are readily dissolved in alcohol, but can be seen in frozen sections and in preparations that avoid alcohol.^2,3  When preserved, they show bright red birefringence under polarized light^2,3  and can be identified by Fourier transform infrared spectroscopy.³ 

It is unclear which dimensions are being measured in the authors' discussion of crospovidone “0.4 to 1.5 mm in diameter” and microcrystalline cellulose “1 to 2.0 mm in diameter.”¹  These are large measurements for microscopically detected material and presumably refer to the entire deposit. We believe this observation requires some clarification, as it would appear to be largely influenced by the size of the foreign material deposit and the completeness of sampling. We have encountered deposits of both materials in pathology specimens that are considerably smaller than the authors' measurements for gastrointestinal deposits,⁴  and as the deposits are not necessarily circular, a measurement of “diameter” appears imprecise.

In the discussion of OsmoPrep, the authors rightly point out that von Kossa is a stain for anionic components (eg, phosphates) of calcium salts rather than a stain for calcium itself.⁵  Therefore, von Kossa reactivity described is not strictly a false-positive (for calcium).