PO:29:144 | Refractory localized pain in fibromyalgia and the importance of differential diagnosis: two cases of Bertolotti’s syndrome and avascular necrosis successfully treated with targeted therapy

Andrea Lacarpia¹, Riccardo Terribili¹, Silvia Valentini¹, Marta Fabbroni¹, Stefano Barbagli¹, Stefano Gentileschi¹, Caterina Baldi¹, Luca Cantarini¹, Bruno Frediani¹ | ¹Azienda Ospedaliera Universitaria Senese, Università degli Studi di Siena, Italy

Background. Fibromyalgia (FM) is a chronic widespread pain condition associated with multiple and heterogeneous systemic manifestations. It is currently regarded as a paradigmatic example of nociplastic pain, specifically a pain not attributable to direct nociceptive stimuli or neuropathic mechanisms, but rather to altered pain modulation processes due to peripheral and central sensitization (hyperalgesia and allodynia). FM may therefore present as a primary condition or coexist with other disorders that can influence its onset, course, and activity. We report two clinical cases of patients with refractory FM in whom an comprehensive diagnostic assessment revealed underlying osteoarticular disorders that responded to targeted treatment, leading to overall symptomatic improvement.

Materials and Methods. The first patient, a 27-year-old woman diagnosed with FM two years earlier (according to the 2016 ACR/EULAR criteria: WPI 9, SSS 11) and with concomitant endometriosis and spasmophilia, complained of mixed low back pain poorly responsive to conservative therapy (amitriptyline, NSAIDs, neurotrophic supplements) and rehabilitation. Lumbosacral MRI revealed a left-sided L5 hemisacralization with hypertrophic transverse process articulating with the sacral ala (Castellvi type IIa), associated with subchondral bone marrow edema—findings consistent with Bertolotti’s syndrome (a lumbosacral transitional anomaly causing chronic low back pain). Intravenous neridronate treatment was initiated (100 mg per infusion, 4 infusions over 12 days). The second patient, a 73-year-old woman with a five-year history of FM (2016 ACR/EULAR criteria: WPI 8, SSS 10) under duloxetine therapy, presented with right hip pain initially attributed to myofascial iliopsoas syndrome in an osteoarthritic context. After failure of local infiltrative therapy, MRI demonstrated early avascular necrosis of the femoral head with subchondral bone edema. Combined treatment was started with intravenous neridronate and hyperbaric oxygen therapy (28 consecutive daily sessions).

Results. In the first patient, pain intensity decreased from 8 to 4 on the VAS scale, with reduced need for NSAIDs and overall improvement in diffuse pain symptoms. In the second patient, VAS pain decreased from 8 to 5, with reduction in nocturnal pain, hyperalgesia, and allodynia, and partial resolution of bone marrow edema. A second combined treatment cycle was planned.

Conclusions. These cases highlight the importance of a complete differential assessment in fibromyalgia patients presenting with refractory localized pain. The identification of coexisting structural conditions, as in the cases reported, can provide specific therapeutic targets, contributing to symptomatic improvement and better control of central sensitization. An integrated clinical approach—combining fibromyalgia diagnosis with the detection of concomitant somatic pathologies—represents a key strategy to optimize outcomes in patients with complex chronic pain.