# Osseous Sarcoidosis Mimicking Metastatic Disease in a Patient With Longstanding Pulmonary Sarcoidosis: A Case Report

## TL;DR

A patient with long-term lung sarcoidosis had bone lesions initially thought to be cancer, but they were later confirmed as sarcoidosis.

## Contribution

This case report highlights osseous sarcoidosis mimicking metastatic disease and emphasizes the need for tissue confirmation in indeterminate imaging findings.

## Key findings

- Osseous sarcoidosis can present with sacral and iliac bone lesions resembling metastatic malignancy.
- Low FDG uptake on PET-CT and biopsy results confirmed sarcoidosis rather than cancer.
- Conservative treatment improved symptoms, and the patient remained stable under surveillance.

## Abstract

Sarcoidosis is a multisystem granulomatous disease in which osseous involvement is uncommon and most often affects the small bones of the hands and feet, whereas axial skeletal disease remains underrecognized and may mimic metastatic malignancy. A 72-year-old man with longstanding pulmonary sarcoidosis and moderate persistent asthma was incidentally found to have multifocal sacral and iliac bone lesions on lumbar spine magnetic resonance imaging (MRI) obtained for evaluation of back pain and radiculopathy. These lesions were radiologically suspicious for osseous metastases, prompting systemic staging with fluorodeoxyglucose positron emission tomography-computed tomography (FDG PET-CT) and referral to hematology/oncology. PET-CT demonstrated low-level FDG uptake within the sacral and iliac lesions, diffuse splenic hypermetabolism, and calcified mediastinal and hilar lymph nodes compatible with prior granulomatous disease, but no hypermetabolic lymphadenopathy or dominant osseous mass. CT-guided biopsy of a left iliac crest lesion revealed focal non-necrotizing granulomas negative for acid-fast bacilli, fungal organisms, and malignancy, establishing the diagnosis of osseous sarcoidosis in the context of systemic disease. The patient’s back pain improved with conservative measures, and he remained without progressive pulmonary or skeletal symptoms under multidisciplinary surveillance. This case highlights that vertebral and pelvic bone lesions in older patients with granulomatous lung disease may represent sarcoidosis rather than metastatic cancer and underscores the importance of tissue confirmation when imaging findings are indeterminate.