Post SARS-CoV-2 infection reactive arthritis: a brief report of two pediatric cases

An 8-year-old previously healthy boy was referred to the pediatric rheumatology center of Kerman University, in Southeast of Iran, for left side lower extremity gait disturbance and limping. This condition had appeared three weeks prior to his visit and he did not have any history of trauma or vigorous activity. However, he had experienced mild respiratory tract infection including low-grade fever and cough approximately one week before refusing to walk. During this time, he had visited an orthopedist. However, his condition was not diagnosed in that visit. Finally, he was referred to our clinic for more evaluations. At the time of his first visit, the patient did not have a fever. We performed a complete and systematic examination. He had an antalgic gait at his left side due to difficulty in weight bearing. His physical examination revealed pain and limitation in flexion, internal and external rotational movements of left hip with a positive FABER Test. There was not any evidence of other contributing factors and red flags, including organomegaly, lymphadenopathy, skin lesions, and neurological deficits. His laboratory evaluations revealed a White Blood Cell (WBC) count of 9\(\times\)10⁹ /L with an Absolute Neutrophil Count (ANC) of 3.2 \(\times\)10⁹ /L and an Absolute Lymphocyte Count (ALC) of \(4.64\times\)10⁹ /L, a platelet count of 312,000/µL, and a hemoglobin of 15.5 g/dl. The Erythrocyte Sediment Rate (ESR) and C-Reactive Protein (CRP) were 3mm/h and 3.5 mg/L, respectively (Table 1). Considering the preceding symptoms of fever and cough, a serological investigation for both IgM and IgG of SARS-CoV-2 infection was performed. The tests indicated a high IgM level of 3.4 (with a 1.1 cut off) in the first test, and a high IgG level of 3.8 (with a 1.1 cut off) in the second test, which was performed one week later. Detection of SARS-CoV-2 antibodies was performed using SARS-CoV-2 immunoglobulin M (IgM) ELISA kits (Pishtaz Teb, Iran, http://​pishtazteb.​com) and SARS-CoV-2 IgG ELISA kits (Pishtaz Teb, Iran http://​pishtazteb.​com) according to the manufacturer’s protocol (Specificity: 97.30 %; Sensitivity: 79.40 %) [11]. The nasopharyngeal swab for coronavirus Polymerase Chain Reaction (PCR) assay was not tested due to latency evaluation from preceding symptoms and patient’s parents refusal. There was not any evidence of marked joint space widening, reactive bone and fatty changes and other pathologic findings in his hip X-Ray. In addition, his chest radiography was normal. He underwent hip joints ultrasound study with a result of 7mm effusion in left side. Finally, Magnetic Resonance Imaging (MRI) showed a moderate joint effusion at his left hip articulation and a minimal joint effusion at his right hip joint (Fig. 1). Treatment was administered by skin traction and Naproxen 250 mg twice a day. The patient consequently recovered approximately one week later without any issues with either hip movement restriction or gait pattern and mobility.

A 6-year-old girl, who had experienced a high-grade fever for two days approximately one week prior to her visit, was referred to our outpatient Clinic due to her left side lower extremity limp. She complained of polyartheralgia in several joints including both knees and wrists with a predominant left lower limb pain in groin region and knee. She was born from a consanguineous marriage from a repeat cesarean section with a birth weight of 2.7 Kg. She had a history of right side hydronephrosis, which had gradually improved. The patient also had a history of limping three years ago, which had led to her hospitalization and aspiration of the right hip joint fluid. She had been unsuccessfully treated for septic arthritis by an orthopedic surgeon. Her mother is a nurse, who had been working in a secondary hospital facility for COVID-19 patients. At the time visit, the patient was thoroughly examined; she did not have fever and her vital signs were within the normal range. She could not bear weight on her lower left limb and had an antalgic gait. During examination, she showed no evidence of muscle involvement, but she had some limitations in the range of movements of her left hip joint and scant tenderness in both wrists. Despite the hip joint involvement, she did not have any compensatory gait pattern, any other limitations such as knee flexion, or any remarkable foot and ankle positioning. Her laboratory evaluation were as followings: WBC: 9.68\(\times\)10⁹ /L (Neutrophils = 5.69 \(\times\)10⁹ /L & Lymphocyte = \(2.65\times\)10 ⁹ /L), platelet count: 511,000/µL, Hemoglobin: 11.9 g/dl, ESR = 39mm/h and CRP = 12 mg/L. She also tested positive for Coronavirus using PCR analysis. Serological investigation for both IgM and IgG of SARS-CoV-2 infection revealed a mild increase in IgM level to 1.2 (with a 1.1 cut off) without increasing the IgG level [11] (Table 1). Further hip X-Ray was normal. The hip ultrasound showed evidence of mild joint effusion in both hip joints especially in the anterior part of her left side (Fig. 2). This patient was also diagnosed with post coronavirus reactive arthritis, and successfully treated with Ibuprofen 40 mg/kg/day administered in three doses during the day. She completely recovered and her laboratory and ultrasound findings became normal after 4 days. Her follow up at least for 45 days later did not show any subsequent signs or sequels.