1) Acute Rejection, Grade A2 2) Microcrystalline Cellulose Emboli David M. Hwang University Health Network Toronto, Ontario, Canada

Clinical History: This 24-year-old patient with cystic fibrosis was admitted for a pulmonary exacerbation. Co-morbidities at the time of admission included pancreatic insufficiency, diabetes, and gastroesophageal reflux, and he had been experiencing generally declining health over the past 3-4 years. He suffered multiple complications while admitted, including pneumothorax related to central line insertion, and recurrent line sepsis and Candidemia while on total parenteral nutrition. He was referred for lung transplant assessment after several months in hospital and underwent bilateral lung transplantation several weeks thereafter. The post-operative course was largely uneventful, apart from some issues with persistent air leak and with pain control. The patient underwent protocol bronchoscopy with transbronchial biopsies at 2 weeks post-transplant, from which H&E and GMS-stained sections are appended. Pathological/Microscopic Findings and any Immunohistochemical or Other Studies: Sections of the transbronchial biopsies showed patchy inflammatory infiltrates composed predominantly of lymphocytes and plasma cells. Occasional concentric perivascular infiltrates containing occasional eosinophils were present, consistent with grade A2 acute rejection. Also present were inconspicuous deposits of pale-staining crystalline material within small blood vessels, without evidence of foreign-body granulomatous reaction. These deposits were birefringent under polarized light, and stained positive with methenamine silver and Congo Red stains. Slide 1 Click to view with ImageScope Click to view with a Web-Based Viewer Slide 2 Click to view with ImageScope Click to view with a Web-Based Viewer Figure 1 Perivascular infiltrates consistent with acute rejection, grade A2 Figure 2 Focal deposit of pale-staining crystalline material. Figure 3 The crystalline material demonstrates birefringence under polarized light. Figure 4 Methenamine silver staining of the crystalline material. Figure 5 Congo Red staining of the crystalline material. Figure 6 Additional crystalline material with foreign body granulomatous response in a 3-month post-transplant transbronchial biopsy. Figure 7 3-month transbronchial biopsy under polarized light. Figure 8 Similar intra- and perivascular crystalline material in the patient's explanted native lungs, with granulomatous reaction and focal destruction of the pulmonary arterial wall. (Elastic trichrome stain) Differential Diagnoses: The differential diagnosis for birefringent crystalline material in the lung could include both endogenous materials (e.g. calcium oxalate) and exogenous materials (e.g. talc, microcrystalline cellulose, starch, or barium), which may enter the lung by inhalation, aspiration, or intravenous injection. Final Diagnosis: 1) Acute rejection, grade A2 2) Microcrystalline cellulose emboli Case Discussion and Review of Literature: This lung transplant recipient was found to have intravascular crystalline material in a routine two-week post-transplant transbronchial biopsy. The characteristics of this material, including its particle size variation (25-200 µm), translucent colorless to pale blue-grey staining in H&E sections, birefringence under polarized light microscopy, and positive staining with GMS and Congo Red, are in keeping with microcrystalline cellulose[1]. Microcrystalline cellulose may also demonstrate focal staining with periodic acid Schiff stain, which was not seen in this case. The primary differential diagnostic consideration based on H&E findings is with intravenous talcosis. However, although strongly birefringent under polarized light, talc crystals appear as irregular needle-shaped or plate-like crystals that are clear and almost colorless to pale-yellow in standard H&E sections, and that do not stain with GMS, Congo Red, or PAS [1, 2]. Both microcrystalline cellulose and talc typically elicit brisk granulomatous reactions. The differential diagnosis theoretically also includes other birefringent materials that may be seen as microvascular emboli in the lungs, although these appear quite different histologically than either microcrystalline cellulose or talc. Starch granules demonstrate birefringence and positive staining with PAS and GMS, but typically have a rounded rather than rod- or needle-like shape, and show a characteristic Maltese Cross pattern under polarized light, with the center of the cross seen centrally in the particle for corn starch, or eccentrically for potato starch [2]. Magnesium stearate is identified less commonly, and appears as irregular, rounded particles measuring 5-10 µm and demonstrating a yellowish birefringence under polarized light [2]. Both starch and magnesium stearate are less frequently associated with granulomatous reaction [2, 3]. The presence of microcrystalline cellulose in the lungs most commonly results from intravenous injection of dissolved oral medications [1, 2, 4, 5, 6, 7, 8, 9], or less frequently as a result of aspiration [10]. In addition to the pharmacologically active agent, tablets prepared for oral use often contain other filler materials, some of which are insoluble, and which act as binders (such as microcrystalline cellulose), lubricants, or disintegrants. In addition to microcrystalline cellulose and other tablet excipients discussed above, pulmonary embolization of crospovidone has also been described [11, 12]. Crospovidone is a disintegrant that has a characteristic coral-like appearance with dark basophilic staining in H&E sections. While it stains positive for Congo Red, crospovidone unlike microcrystalline cellulose is non-birefringent and stains only weakly with methenamine silver stains [11]. Intravenous injection of tablets intended for oral use may result in a spectrum of pathologic findings in the lungs, including vascular, perivascular and interstitial foreign body granulomas, angiothrombotic lesions, emphysema, diffuse interstitial fibrosis, and even progressive massive fibrosis-like lesions [13, 14]. Radiologic findings are most commonly of diffuse interstitial and centrilobular nodules [6, 12, 13, 15, 16]. Clinically, patients may present with features of pulmonary hypertension [1, 4, 6, 17, 18], or with accelerated deterioration of pre-existing lung diseases such as cystic fibrosis [12]. In the setting of a lung transplant recipient, identification of tablet excipient material in an allograft biopsy could reflect undiscovered drug use in the organ donor, but may equally indicate substance abuse by the recipient [9, 19]. In the present case, review of the patient's native lungs showed bronchiectasis and secondary features consistent with the history of cystic fibrosis. Intravascular, perivascular, and interstitial deposits of microcrystalline cellulose were noted throughout both lungs, associated with focal thrombosis. Foreign body granulomatous reaction was present, associated in some areas with destruction of arterial walls. Review of the patient's pre-operative echocardiogram found evidence of mild pulmonary hypertension, with mild right ventricular enlargement and estimated right ventricular systolic pressure of 45 mm Hg. The lack of granulomatous response in the patient's two week post-transplant allograft biopsy was suspicious for recent intravenous injection, particularly given the finding of cellulose granulomatosis in the patient's explanted lungs. A follow-up allograft transbronchial biopsy at 3 months post-transplant showed markedly increased deposits of microcrystalline cellulose compared to the 2-week biopsy, some of which were associated with a foreign body granulomatous response. When confronted by clinical staff regarding the suspicion of substance abuse, the patient admitted to injecting dissolved opioid tablets through his central venous catheter, both before and after transplantation, including during his two-week post-operative course in hospital. Psychiatric referral was made for further evaluation and management of substance abuse issues. Conclusions: -Pathologists should be mindful that important entities other than rejection or infection may be encountered in biopsies performed for routine lung allograft monitoring. -Intravenous injection of dissolved tablets intended for oral administration may result in intrapulmonary emboli of insoluble pill excipient materials such as microcrystalline cellulose, talc, starch, crospovidone, and magnesium stearate. Differentiation of these entities is possible based on morphologic, birefringence, and staining characteristics. References: Tomashefski JF Jr, Hirsch CS, Jolly PN. Microcrystalline cellulose pulmonary embolism and granulomatosis. A complication of illicit intravenous injections of pentazocine tablets. Arch Pathol Lab Med 1981;105:89-93. Kringsholm B, Christoffersen P. The nature and the occurrence of birefringent material in different organs in fatal drug addiction. Forensic Sci Int 1987;34:53-62. Kringsholm B, Christoffersen P. 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