Not all back pain is created equal

A 74-year-old female was referred from outpatient orthopaedic clinic for an MRI spine after presenting with groin, back and hip pain on mobilisation. Past medical history included osteoarthritis, right total hip replacement and previous hysterectomy.

Initial MRI spine showed rounded T1 low signal bone marrow foci throughout the whole spine suspicious for metastatic deposits without cortical breakthrough, cord compression or canal stenosis.

Follow up CT Thorax, Abdomen and Pelvis showed multiple bilateral pulmonary nodules, with a dominant 13mm right upper lobe nodule and ipsilateral mediastinal lymphadenopathy, measuring up to 15mm in the right lower paratracheal station together with smaller hilar lymph nodes. Multiple sclerotic lesions were confirmed throughout the axial skeleton. There was no intra-abdominal disease.

CT-guided percutaneous biopsy of an L2 sclerotic lesion gave the diagnosis.

Sarcoidosis is well known as the ‘great mimic’ and the path to diagnosis is not always a straightforward one. Between one-third and one-quarter of people with sarcoidosis have some form of musculoskeletal involvement, most commonly presenting as small joint arthropathy [1]. Bone involvement is thought to be less common, occurring in an estimated average of 5% of patients [2]. It is postulated however, that the prevalence of osseous sarcoid is much higher owing to the fact that it is most often asymptomatic [3, 4] and remains undetected unless patients undergo advanced imaging. In this case osseous sarcoid was the primary cause for presentation, which is a rare occurrence given its tendency to develop later in the disease, when other systemic manifestations are more likely to already be present [3, 4, 5].

The imaging appearances of bone involvement are many with no specific pattern to rely upon and these often emulate that of a neoplastic process. Bone lesions can show increased uptake on technetium bone scan. On CT imaging these may be destructive, sclerotic or even undetectable [6]. Lesions have variable marrow signal changes on MRI[2][5], with no reliable discriminators to accurately differentiate sarcoidosis from malignancy [6]. Therefore, histological evidence is pivotal in making a diagnosis [7, 8]. Pursuing and ruling out more common pathologies, such as metastatic malignancy, should usually take precedence especially if there is not already an established diagnosis of sarcoidosis.

In this case, the patient’s presenting complaint was groin, hip and back pain. Following the initial MRI spine and subsequent CT, the patient was discussed in both Cancer of Unknown Primary and Lung cancer Multidisciplinary Team Meetings (MDT). The main differential diagnoses were that of metastatic cancer or lymphoma. An Endobronchial Ultrasound (EBUS) guided biopsy of a 4R lymph node was inadequate and the right upper lobe nodule was deemed unsuitable for biopsy. A lesion in the left upper portion of L2 was the next best option for tissue diagnosis. Histology revealed necrotizing granulomata in keeping with sarcoidosis and the patient was commenced on corticosteroid therapy.

At 6 months follow up, the patient was still on a tapering course of Prednisolone, and her symptoms did not mandate any dedicated follow up of her spinal lesions. These are, however, still visible on the only subsequent imaging performed at the time, a High Resolution Computed Tomography (HRCT) of her thorax, and had not yet regressed.

All patient data have been completely anonymised throughout the entire manuscript and related files.