Abstract
Varicella-zoster is a common paediatric viral infection that usually runs a benign self-limiting course but has a risk of complications. The most common sequelae are bacterial skin infections, which are usually mild. However, bacteraemia/septic shock, toxic shock syndrome, pneumonia, ataxia, encephalitis and purpura fulminans are also possible. Although rare, musculoskeletal sequelae (osteomyelitis, septic arthritis, pyomyositis and necrotizing fasciitis) can occur in otherwise healthy children. These latter complications are potentially life- and limb-threatening and must be considered in a child post-varicella with pain in a limb or joint. We describe two patients who had musculoskeletal complications after varicella: (1) a 16-month-old boy who developed pyomyositis of the thigh and septic arthritis of the hip and (2) a two-year-seven-month-old girl who developed septic arthritis of the hip and knee and a ‘bare area’ subperiosteal abscess of the femur. Their clinical presentations, detailed management plans and outcomes are reported. These cases highlight the importance of prompt diagnosis, appropriate investigation (including the important role of magnetic resonance imaging) and surgery when an otherwise healthy post-varicella child deteriorates.
Introduction
Varicella-zoster is a common paediatric viral infection that usually runs a benign self-limiting course but has risk of complications. The most common sequelae are bacterial skin infections, which are usually mild. 1 However, bacteraemia/septic shock, toxic shock syndrome (TSS), pneumonia, ataxia, encephalitis and purpura fulminans are also possible.2–4 Although rare, musculoskeletal sequelae (osteomyelitis, septic arthritis, pyomyositis and necrotizing fasciitis) can occur in otherwise healthy children.5–10 These complications are potentially life- and limb-threatening and must be considered post-varicella if there is pain in a limb or joint.5,6
We describe two patients who had musculoskeletal complications after varicella: (1) a 16-month-old boy who developed pyomyositis of the thigh and septic arthritis of the hip and (2) a two-year-seven-month-old girl who developed septic arthritis of the hip and knee and a ‘bare area’ subperiosteal abscess of the femur. These two cases highlight the importance of prompt diagnosis, appropriate investigation (including magnetic resonance imaging [MRI]) and surgery.
Case presentation 1
A 16-month-old boy presented 10 days after the onset of varicella with generalized oedema, pyrexia, respiratory distress and anuria. He needed intravenous inotrope support (dopamine 60 μg/min, noradrenaline 1 μg/min, adrenaline 1.2 μg/min and vasopressin 0.045 U/h). Two days after admission, he developed a tense erythematous swelling in the right forearm.
His right hand was fully extended at metacarpophalangeal joints, fully flexed at interphalangeal joints with high compartment pressures (extensor, 45 mmHg; flexor, 30 mmHg) suggestive of compartment syndrome. Left arm and both legs were soft and passive movement did not indicate a problem elsewhere. Although no organism was cultured from swabs, it seems likely that the compartment syndrome was due to an infective aetiology secondary to Varicella-zoster infection. Broad-spectrum intravenous antibiotics (benzylpenicillin 500 mg 4 times daily, clindamycin 100 mg 4 times daily and gentamicin 70 mg once daily) were commenced and an emergency right forearm fasciotomy was performed. Intraoperatively, the muscles were oedematous but viable (wound closure occurred after 3 days).
Eight days after closure, he remained unwell and developed a painful, erythematous right proximal thigh. Ultrasound showed a 5 mm hip effusion. He underwent an urgent right hip aspiration which showed frank pus and immediately proceeded to arthrotomy and washout. One day postoperatively, MRI showed a significantly subluxated right femoral head (Figure 1), further fluid collection and pyomyositis. A repeat arthrotomy/washout was performed with subsequent spica cast immobilization with the femoral head reduced on arthrogram (Figure 2).
Coronal MRI scan (T2-TSE SPAIR sequence) showing hypoperfused right femoral head and subluxated right femoral head
Intraoperative arthrogram showing the femoral head to be enlocated on hip flexion (90°) and abduction (45°)
He improved and was discharged after three weeks with oral antibiotics (clindamycin 60 mg 4 times daily and penicillin V 125 mg 4 times daily). The spica cast was maintained for three months with a change at six weeks. At five months, he had a 1 cm shortened right hip, no flexion deformity, a good range of movement and was walking well. He had full function of his right arm and hand with a good range of movement. Radiographs (Figure 3) at eight months showed avascular necrosis and destructive changes to his right hip joint.
Radiographs of the pelvis showing avascular necrosis and destructive changes to both sides of the right hip joint (right) anteroposterior (left) frog lateral
Case presentation 2
A two-year-seven-month-old girl was admitted with a febrile convulsion secondary to Varicella-zoster (appearing three days before presentation). She was lethargic, had a high temperature (40°C) and was not eating or maintaining fluid intake. On examination, she was irritable with florid varicella lesions over her face, back and trunk (legs were spared). She was tachycardic (183 beats/minute), tachypnoeic (38 breaths/minute) with normal tone in all four limbs and full range of movement. She had positive nitrites, microscopic haematuria and proteinuria on urine dipstick and was treated for presumed urinary tract infection (urinary sepsis) on admission. She was started on intravenous antibiotics (co-amoxiclav 420 mg 3 times daily) for her skin infection and presumed urinary tract infection. A right ear swab showed Group A Streptococcus (GAS) on the following day. Over the subsequent two days, she became increasingly unwell, developing an acutely tender and swollen right knee and thigh, prompting referral to orthopaedics. There was no erythema or skin changes. Her right hip was held in flexion (45°), and she would not tolerate passive movement from this position. She was extremely tender and distressed on light palpation of her thigh, hip and posterior aspect of her knee. She had a full range of movement at her right knee and ankle as well as her contralateral leg.
Radiographs (Figure 4) were suggestive of femoral osteomyelitis. She was started on triple broad-spectrum intravenous antibiotics therapy (flucloxacillin 750 mg 4 times daily, clindamycin 95 mg 4 times daily and benzylpenicillin 750 mg 4 times daily) while awaiting blood culture results. She underwent urgent aspiration and washout of her right hip and knee showing purulent synovial fluid at both sites. The arthrotomy and washout of her right hip (anterior approach) showed a thickened hip capsule with purulent synovial fluid. An extensive arthroscopic washout of the knee was also performed.
Lateral radiograph of the femur showing an area of lucency in the posterior aspect of distal femoral metaphysic but no sign of cortical breach
On day 4, she had improved clinically and appeared more comfortable. Microscopy results from aspirated synovial fluid showed Gram-positive cocci and urine culture showed lactose-fermenting coliforms. She underwent a further aspiration and washout of her right hip and knee.
On day 5, MRI under general anaesthesia showed near whole right femoral involvement (heterogeneous bone marrow signal abnormality and patchy contrast enhancement within the medullary canal of the femoral diaphysis and distal metaphysis). There was a cortical breach at the posteromedial aspect of the distal femoral metaphysis. A subperiosteal collection measuring 10 cm × 2.5 cm × 1 cm down the posterior aspect of the right femoral diaphysis (Figure 5) extended distally to the level of the growth plate. There were marked circumferential soft tissue swelling and patchy contrast enhancements extending up to the lateral margin of the right ilium with a small volume of free fluid seen in the pelvis. These were suggestive of right femoral osteomyelitis with a large associated subperiosteal collection. There was no right leg deep venous thrombosis on Doppler ultrasound.
Transverse MRI scan (STIR-TSE sequence) showing subperiosteal collection at the posterior aspect of the right femoral diaphysis
A repeat washout of the right hip showed no re-accumulation, but washout of the right knee showed some turbid fluid. Surgical drainage of the femoral abscess was carried out via a posterolateral approach and 50 mL of purulent fluid was drained. After copious washout, a corrugated drain was inserted and the wound was left open around this (i.e. extensions closed). Two days later, a further washout of the right thigh and knee preceded closure of both wounds (no pus detected). Her clinical condition improved steadily, her right thigh became non-tender with a full range of movement and the ability to bear weight following four-weeks course of intravenous antibiotics. She was discharged on a sixweeks course of oral antibiotics (co-amoxiclav 125/31 suspension 3 times daily).
At three weeks after closure, there was new bone formation posterior to the femoral shaft (Figure 6) with several lucencies in the distal metaphysis. At two months review, she was clinically well with no focal tenderness throughout the right leg with a full range of movement at knee and hip. At six months review, the radiograph (Figure 7) showed continued re-modelling along the posterior femoral shaft with residual minor irregularity in the metaphysis consistent with progressive healing and no signs of early physeal closure.
Lateral radiograph of femur showing new bone formation posterior to femoral shaft with several areas of lucencies in the distal metaphysic
Lateral radiograph of right femur showing continued remodelling of the posterior femoral shaft
Discussion
Varicella-zoster virus (VZV) is the cause of chicken pox, a common paediatric disease with over 90% of cases occurring in children younger than 10 years. It is usually acquired from inhalation of the contaminated respiratory droplets. Viral transmission may also occur due to direct contact with vesicles from an infected individual, but the risk is lower. After inhalation, the virus colonizes and infects the upper respiratory tract and viral replication starts in the regional lymph nodes draining the upper respiratory tract within 2–4 days. Four to six days later, primary viraemia occurs with spread to the reticuloendothelial system (mainly the spleen and liver). At 14–16 days, a secondary viraemia is characterized by the appearance of the characteristic vesicles (resulting from the diffuse viral infection of the capillary endothelial cells and the epidermis). Following primary infection, VZV remains dormant in the dorsal ganglion cells of the sensory nerves. 11
In an otherwise healthy child, varicella is usually a benign self-limiting disease with infectious complications known to occur mostly in infants and toddlers.12,13 The most common complication is skin infection, but other complications include bacteraemia/septic shock, TSS, pneumonia and encephalitis.2,3,13,14 In an epidemiological study by Choo et al. 15 there was an overall complication rate of 205 per 10,000 cases (2.05%) within 30 days after the onset of primary varicella. Although uncommon, postvaricella musculoskeletal complications can be limb- and life-threatening. Schreck et al. 9 calculated the approximate rate of one musculoskeletal complication for every 10,000 (0.01%) paediatric varicella cases. Several authors have reported a variety of post-varicella-associated musculoskeletal sequelae, including purpura fulminans, 16 septic arthritis,8,9,17–20 osteomyelitis,5,6,9,10,21–25 deep-tissue abscess, pyomyositis9,25 and necrotizing fasciitis.7,9,25 Patients with necrotizing fasciitis or pyomyositis often develop life-threatening complications of TSS. 25
Two major bacteria implicated for post-varicella infection are Group A β-haemolytic streptococcus (GABHS) and Staphylococcus aureus.3,9,14,15 The commonest organism involved in non-varicella-associated osteomyelitis and septic arthritis is S. aureus. 26 In contrast, GABHS appears to be the predominant cause for musculoskeletal complications after varicella infections in several case series.3,9,10,27,28 An exception is the case series of Fleisher et al. 17 in which S. aureus was the main causative organism for secondary soft-tissue bacterial infection. Secondary bacterial infections occur after the disruption of the protective skin barrier through the varicella vesicle and possibly by virus-induced alterations of immune functions. 14 Another contributing factor is trauma to skin from scratching that could lead to bacteraemia. 9 GABHS possesses tissue-dissolving enzymes (hyaluronidase and streptolysin) that facilitate penetration of deeper tissues. 29 The incidence and severity of GABHS infection appears to be increasing.5,25,30
In our two cases, both patients experienced a rapid deterioration in their clinical conditions. The physician must remain alert for musculoskeletal complications after varicella. The treatment of both osteomyelitis and septic arthritis is based on antibiotic therapy in combination with urgent surgical drainage.
Conclusions
The rapid deterioration of an otherwise healthy child after varicella infection should raise suspicion of occult musculoskeletal infections requiring urgent surgical consultation and management. These two case reports both show the important role of MRI, even after drainage of septic arthritis. In the first case, a subluxated hip which would otherwise not have been suspected at such an early stage was demonstrated. In the second case, a large subperiosteal abscess was defined allowing surgical management. GABHS should be considered as a causative organism as it is the most common organism involved for post-varicella musculoskeletal complications. Bare area abscesses require surgical drainage for effective management. Spica cast immobilization to contain the subluxated femoral head was used in our case.