We present the case of a 55-year-old patient who was referred to our chronic pain unit for low back pain of more than 2 years' duration. The patient had undergone surgery 17 years earlier for the implantation of a mitral valve prosthesis and since then had presented periprosthetic leakage, with mild haemolysis, on treatment with iron, folic acid and anticoagulated with anticoagulants.
The subject reported continuous baseline pain in the lower back, of mild intensity, with a score of 3 on the visual analogue scale, with exacerbations up to a score of 8, predominantly at night and almost daily. The pain was located in the dorsolumbar area with irradiation towards the inguinogenital area, more pronounced on the right side, but affecting both sides. The duration of these episodes varied from minutes to hours, with the patient comparing it to a burning sensation and stiffness. There was discrete improvement with exercise. He reported no other symptoms, such as paresthesia or sleep disturbances.
On examination, he had no limitation of spinal mobility, mild pain on flexion and negative arc sign, and non-painful palpation of the spinous processes. Trigger points were identified in the paravertebral area, most relevant in the musculature corresponding to the right quadratus lumborum muscle; tests for involvement of the psoas and the right sacroiliac joint were positive. There was no sensory impairment.
Magnetic resonance imaging (MRI) of the dorsolumbar muscle spine reported "polydiscopathy with degenerative changes at L4-L5, L5-S1 (decreased T2 signal intensity of the discs), no significant disc imprints over the spinal canal and signs of dorsolumbar interapophyseal arthrosis". Haemoglobin was 10 g/dl.
The estimated clinical judgement was dorsalgia and low back pain secondary to a myofascial syndrome and degenerative polydiscopathy. Medical treatment was started with pregabalin, tramadol and paracetamol; he received transcutaneous electrotherapy. Corticosteroid and local anaesthetic infiltration of the trigger points corresponding to the right lumbar quadratus lumborum muscle and bilateral lumbar facets was performed; none of the therapeutic measures improved the low back pain. He was then treated with transcutaneous fentanyl; the patient noted a slight improvement.
The subject was re-evaluated after 3 months of treatment. Blood tests showed an increase in haemolysis parameters: decrease in haemoglobin (9.6 g/dl), haemoglobinuria 250 erythrocytes/field, elevated lactodehydrogenase (LDH 4,806 U/l) and total bilirubin 4.38 mg/dl. Echocardiography showed ventricular dilatation and severe mitral stenosis with perivalvular leak and elevated pressure gradient. The patient was referred to the cardiovascular surgeon and underwent surgery to replace the malfunctioning prosthetic valve.
After the operation, one year later, the patient remains free of low back pain.

