A 73‐year‐old man presented with fever, polyarthritis and erythema on his back (Figure 1A) and extremities (Figure 1B). Laboratory findings showed leukocytosis and elevated CRP (24 mg/dL), white blood cell (11 800/μL; neutrophil (88%)), GOT (78 U/L), GPT (89 U/L), LDH (382 U/L), ferritin (1023 ng/mL) and IL‐6 (143 pg/mL). Autoantibodies were all negative. Contrast enhanced CT revealed swollen mediastinal lymph nodes and pericardial effusion. Gastrointestinal endoscopic examinations showed no specific findings. FDG‐PET/CT demonstrated high FDG uptake in mediastinal lymph nodes (Figure 1C–E), multiple joints (Figure 1C), and pericardium (Figure 1F). These clinical, laboratory and imaging findings indicated adult‐onset Still's disease (AOSD)‐like manifestations and possible malignancy despite no organ lesions. In order to differentiate the possibility of paraneoplastic AOSD, thoracoscopic mediastinal lymph node biopsy was performed. Biopsy specimen suggested adenocarcinoma (Figure 1G) with EGFR gene mutation and positive immunostaining of IL‐6 (Figure 1H), CK7 (Figure 1I), and TTF‐1 (Figure 1J). Thus, he was diagnosed with paraneoplastic AOSD caused by IL‐6‐producing mediastinal lymph node carcinoma of unknown primary site, most likely lung adenocarcinoma. Treatment with osimertinib, EGFR inhibitor, was initiated, resulting in the remission of clinical manifestations and the improvement of laboratory and imaging findings.
FIGURE 1.
Gross appearance of back and lower extremity showed erythema (A) and arthritis (B). FDG‐PET/CT demonstrated high FDG uptake in mediastinal lymph nodes (C–E), multiple joints (C), and pericardium (F). Lymph node biopsy suggested adenocarcinoma (G) with positive immunostaining of IL‐6 (H), Cytokeratin 7 (CK7) (I), and Thyroid transcription factor‐1 (TTF‐1) (J).
Paraneoplastic syndrome mimicking AOSD is a rare condition with only a limited number in the literature [1, 2]. Previous reports have suggested that paraneoplastic cases may occur in relatively older patients. As the present case indicates, IL‐6 production by carcinoma might cause AOSD‐like manifestations.
Lymphadenopathy is often revealed in AOSD patients, while adenocarcinoma of unknown primary in a mediastinal lymph node is rarely reported [3, 4].
Therefore, clinicians always need to note the possibility of adenocarcinoma of unknown primary in a mediastinal lymph node when the patients show AOSD‐like manifestation, and FDG‐PET/CT should be recommended to screen for occult malignancy in elderly patients presenting with AOSD‐like manifestations.
Author Contributions
Y. Taniguchi and D. Okada equally contributed to this manuscript.
Funding
The authors have nothing to report.
Conflicts of Interest
The authors declare no conflicts of interest.
Acknowledgments
We would like to thank Editage (www.editage.jp) for English language editing.
Data Availability Statement
Data sharing not applicable to this article as no datasets were generated or analysed during the current study.
References
- 1. Neishi J., Tsukada Y., Maehara T., Ueki K., Maezawa A., and Nojima Y., “Adult Still's Disease as a Paraneoplastic Manifestation of Breast Cancer,” Scandinavian Journal of Rheumatology 29 (2000): 328–330. [DOI] [PubMed] [Google Scholar]
- 2. Wu N., Li Q., Gu C. X., Ahmed T., and Yao X. P., “Paraneoplastic Syndrome Mimicking Adult‐Onset Still's Disease by Advanced Lung Cancer: A Case Report,” BMC Cancer 11 (2011): 487. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 3. Kawasaki H., Arakaki K., Taira N., et al., “Lung Cancer Detected 5 Years After Resection of Cancer of Unknown Primary in a Mediastinal Lymph Node: A Case Report and Review of Relevant Cases From the Literature,” Annals of Thoracic and Cardiovascular Surgery 22 (2016): 116–121. [DOI] [PMC free article] [PubMed] [Google Scholar]
- 4. Stewart J. F., Tattersall M. H., Woods R. L., and Fox R. M., “Unknown Primary Adenocarcinoma: Incidence of Overinvestigation and Natural History,” British Medical Journal 1 (1979): 1530–1533. [DOI] [PMC free article] [PubMed] [Google Scholar]
Associated Data
This section collects any data citations, data availability statements, or supplementary materials included in this article.
Data Availability Statement
Data sharing not applicable to this article as no datasets were generated or analysed during the current study.