Microcrystalline cellulose (MCC) is extensively used as a filler material in pharmaceutical tablets. When injected intravenously in aqueous tablet suspensions, MCC may contribute to embolic pulmonary hypertension and be identified histologically in lung tissue samples. In this study, we evaluated a modified Russell Movat pentachrome stain (MMPS) as a means of recognizing MCC and distinguishing it from other birefringent crystals in lung specimens.
To study the staining properties of MCC versus other crystalline materials using the MMPS stain.
Archival, formalin-fixed, paraffin-embedded lung specimens that contained birefringent crystals, including MCC (3 cases of intravenous drug abuse), talc (2 cases of intravenous drug abuse, 1 talc pleurodesis), mixed silicates (1 case of silicate pneumoconiosis), and calcium oxalate (1 case of aspergillosis from Aspergillus niger infection), were evaluated with MMPS. Crystal identification was confirmed by morphology, other histochemical stains, infrared spectroscopy (1 case), and cellulose controls.
The MMPS stained the MCC bright yellow in tissue and control specimens. Talc stained light greenish-blue; mixed silicates appeared either greenish-blue or unstained. Oxalate crystals stained sea-green. Crospovidone, a nonbirefringent tablet filler substance, stained yellow to dark green with MMPS and was easily distinguished from MCC. Starch granules were unstained by MMPS.
The MMPS is an excellent method for the histochemical identification of MCC in tissue and its separation from other birefringent crystals with which MCC might be confused. The MMPS is especially useful in the evaluation of pulmonary foreign body embolization in cases of suspected intravenous substance abuse.