American Journal of Respiratory and Critical Care Medicine

To the Editor:

The diagnosis of focal eosinophilic inflammation is notoriously difficult. Here we describe a novel technique using technetium-99m–labeled autologous eosinophils to image eosinophilic vasculitis affecting the lung and skin in a patient with granulomatosis with polyangiitis.

Our patient, a 48-year-old male, presented with cough, purulent sputum, hemoptysis, lethargy, and painful ulcers affecting his hands and feet. His thoracic computed tomography (CT) showed bilateral upper zone nodules with cavity formation. Previously he had experienced recurrent anterior uveitis and small joint polyarthropathy. His medications were hydroxychloroquine and etodolac, which he took intermittently. Examination revealed periungual erythema and multiple deep ulcers affecting his fingers and right ankle (Figure 1A). His blood eosinophil count was 0.76 × 109/L, with normal renal and liver function and normal antinuclear antibody and rheumatoid factor. His antineutrophil cytoplasmic antibody (ANCA) immunofluorescence was positive with a (PR3) ANCA of 25 IU/ml (normal range < 0.2 IU/ml). He also had evidence of IgG4-related disease associated with his ANCA-positive vasculitis with a serum IgG4 of 4.1 g/L. Surgical lung biopsy revealed dense fibrosis, with scattered noncaseating granulomas, heavy eosinophil infiltration, a medium-small vessel vasculitis, and IgG4-staining plasma cells. Similar findings were observed in the skin (Figure 1B).

Technetium-99m–labeled eosinophils (98.5% pure) were prepared using clinical grade anti-CD16 immuno-magnetic beads as described (1) and 16 × 106 cells (187 MBq) reinjected. Dynamic images were taken for 40 minutes (1) followed by single-photon emission CT (SPECT-CT) images at 45 minutes and 2, 4, and 6 hours. His legs were imaged using a γ camera (Figure 1C). The intravascular residence time (1.5 h) of the technetium-99m–labeled eosinophils was much shorter than that observed in healthy subjects (1) with only 4.9% of the injected cells remaining in the circulation at 30 minutes. This compares to an intravascular residence time of indium-111–labeled eosinophils in healthy volunteers of 28.1 ± 1.7 hours (mean ± SEM), with 14.5 ± 2.5% of radiolabeled cells remaining in the circulation at 30 minutes (1). Although the technetium-99m–labeled eosinophils accumulated as expected in the liver, spleen, and bone marrow (Figure 1D), SPECT-CT revealed additional uptake in some but not all of his lung nodules (Figures 1E–1G).

Although radiolabeled leukocyte scanning is used routinely for localizing occult infection, this approach has not been used previously to demonstrate focal eosinophilic inflammation. Advances in immuno-magnetic bead technology have permitted the isolation of ultra-pure nonactivated eosinophils from blood, which are amenable to radiolabeling and behave physiologically when reinjected in healthy subjects (1). Alternative, indirect methods of detecting eosinophilic inflammation in humans, such as exhaled nitric oxide and analysis of breath condensates, are nonspecific and can only assess the inflammatory burden in the respiratory tract. In contrast, technetium-99m–labeled eosinophils plus SPECT-CT can localize focal eosinophilic inflammation directly in vivo. Furthermore, this technique is less invasive than performing bronchoscopy and transbronchial biopsy, which may be contraindicated in some patients and carry significant risk. This novel approach therefore offers the prospect of a noninvasive method to aid in the diagnosis, localization, and assessment of disease activity.

The authors are grateful to Rosalind Simmonds, the staff within the Nuclear Medicine and Histopathology Department at Addenbrooke’s Hospital, and the Wellcome Trust Clinical Research Facility, Cambridge. They acknowledge the help of the Histopathology Departments at the Royal Brompton and Princess Alexandra Hospitals. They also thank the Cambridge Biomedical Research Centre and BRC Core Biochemistry Assay Laboratory and acknowledge the support of the National Institute for Health Research, through the Comprehensive Clinical Research Network. The study was approved by Cambridgeshire Research Ethics Committee (09/H0308/119) and the Administration of Radioactive Substances Advisory Committee of the UK (83/3130/25000).

1. Farahi N, Singh NR, Heard S, Loutsios C, Summers C, Solanki CK, Solanki K, Balan KK, Ruparelia P, Peters AM, et al. Use of 111-indium-labeled autologous eosinophils to establish the in vivo kinetics of human eosinophils in healthy subjects. Blood 2012;120:40684071.

Supported by Asthma-UK [08/11], the Medical Research Council [grant number MR/J00345X/1], the Wellcome Trust [grant number 098351/Z/12/Z], and Cambridge NIHR Biomedical Research Centre.

Author Contributions: N.F. performed experiments and analyzed the data. C.L. performed experiments and analyzed data. A.M.P, A.M.C., and E.R.C. contributed to the design and writing of the study.

Author disclosures are available with the text of this letter at www.atsjournals.org.

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