2.CASE PRESENTATION
A previously healthy 28-year-old Tunisian man was admitted to our Department of internal medicine on april 2022 with a painful swelling of her right knee with more than twelve month history of persistent pain, stiffness and functional disability. Her history revealed that symptoms occured two weeks after the second shot of coronavirus mRNA BNT162b2 (Comirnaty Pfizer–BioNTech) COVID-19 vaccine (the first dose was also Comirnaty)
He was treated with nonsteroidal anti-inflammatory drugs (NSAIDs) without any relief. His pain and disability were worsened to the point that his daily activities were restricted (walk, managing stairs…), and his work was badly compromised.
He reported that pain and weakness were evident the night with an average intensity of 9 on a numeric rating scale (NRS) of 0 to 10.
On examination, the right knee showed mild not pitting edema with tactile allodynia, extreme restriction of knee joint on active and passive movement and major atrophy of the right muscles. There was tactile allodynic response to any palpation on anterior and medial area of the knee The left knee and the upper limbs were both normal.
Blood screening which include a sedimentation rate (4 mm first hour), C-reactive protein (18 mg/l), full blood counts (white blood cell count , hemoglobin level and platelet level) , electrolytes, creatinine, fasting glucose, liver function tests (including Total bilirubin , ASAT and ALAT GGT), creatine phosphokinase were all normal. Serum rheumatoid factor, anti-citrullinated peptides, antinuclear antibodies (ANA), Anti-neutrophil cytoplasmic antibodies (ANCA) and hepatitis B and C viral screening were all negative. The Thyroid stimulating hormone (TSH) value was normal at 0,69 mUI/L. 25-hydroxy vitamin D level was found to be low (17 ng/mL). There was no evidence of obvious infectious and all bacteriological studies were negative. An electromyography of the lower limbs was performed and did not show any pathologic findings.
MRI of the right knee was performed and showed extensive patchy bone marrow edema with high signal within the femur , the tibia and the patella in proton density weighted fat saturated sequences , with a mild joint effusion without fractures lines (Figures 1 and 2).
Therefore, the diagnosis of CRPS of the right knee after COVID-19 vaccination was made.
Many treatments were tried with unsatisfactory pain relief : intra-articular knee injections, pregabalin, opioids. The patient was was managed with extensive and regular physiotherapy including muscle strengthening and functional training. He was started alendronate 70 mg orally twice a week , calcium carbonate - cholecalciferol supplementation with psychotherapy to reduce anxiety
The patient responded very slowly to the treatment and began to show marked improvement in pain, range of movement and function but without complete recovery.
A second MRI was performed 8 months after the diagnosis (Figure 3). It showed a mild dicrease of the signal of the bone marrow edema within the femur and tibia, marked improvement of the edema within the patella; Persistance of the joint effusion. A bone resorption and muscle hypotrophy were observed.