Children with lower limb pain is a relatively common presentation in clinical practice, and can be one of a range of differential diagnoses. It is important that health professionals are able to recognise the clinical presentation of a septic joint and also develop an approach for the initial assessment and management of a child presenting with limb pain (Tse and Laxer, 2006).
Benign acute childhood myositis (BACM) is a relatively rare and transient condition of acute lower limb pain in children, which is manifested by sudden onset of leg pain and tenderness over the calf muscles. It is an under-recognised condition in clinical practice and an area where little research has been done recently. A search of PubMed using the term ‘benign acute childhood myositis’ returned 48 hits, 44 of which were relevant to the topic and all of these were published in medical journals.
BACM usually starts after a period of rest and is characterised by a refusal or inability to walk. It typically occurs after a viral illness, especially after an influenza infection (Mackay et al, 1999; Paul et al, 2017; Szenborn et al, 2018). Although rare, the condition can cause severe pain in the lower extremities, which can debilitate the child for up to 1 week and may cause significant distress to the child and their family (Koliou et al, 2010). A key biochemical marker in BACM is elevated creatine kinase (CK) due to muscle tissue breakdown; however, the condition is self-limiting, generally requiring conservative management only. This article presents the case of a 10-year-old boy with subacute bilateral leg pain following a viral illness, which limited his mobility.
Case study
A previously healthy 10-year-old boy presented to the paediatric assessment unit (PAU) with a 4-day history of bilateral leg pain, which was progressively worsening. There was no change reported in his bowel or bladder habits and he was reported to be fully immunised.
The boy had experienced a brief, flu-like illness with fever, headaches and two episodes of vomiting on the second day of illness. The day before he presented to the PAU, the pain in his legs limited his mobility to such an extent that he was walking on the lateral sides of his feet and eventually started crawling. On the day of presentation, he refused to bear any weight on his legs. The patient reported that the severity of pain when moving his legs was around 9 out of 10, compared with 7 out of 10 during onset. He was given paracetamol and ibuprofen at home for the pain with minimal benefit. There was no reported history of trauma. At presentation in the PAU, a dose of oral morphine was administered.
Initial assessment
The following were noted at the initial assessment undertaken by the paediatric advanced nurse practitioner (ANP):
On examination, the young patient was systemically well. His legs were painful to both touch and movement, especially over the calf muscles, which were not swollen, red or warm to the touch. The pain was relieved when the knees were flexed to a 100° angle. Posterior tibial and dorsalis pedis pulses were palpable on both sides and the feet were warm and well perfused. Neurological testing revealed a slight decrease in the power of the lower limbs, which was deemed likely to be a consequence of the pain and limited effort. Fine touch and vibration sense was normal.
The young patient was admitted with an initial diagnosis of BACM. Other differential diagnoses considered were:
The following investigations were planned by the paediatric ANP in agreement with the consultant paediatrician in order to establish a diagnosis and exclude other serious aetiologies:
Management in hospital
On the day of admission, the patient's blood tests returned with raised CK levels of 3164 IU/litre (range: 24-195) and a serum aspartate transaminase level of 109 IU/litre (range: 10-40); both results were suggestive of possible muscle breakdown. The X-ray of the patient's legs showed no abnormalities. The orthopaedic team reviewed the patient the same evening and an MRI was carried out the following morning. The MRI scan was reported as normal.
A diagnosis of BACM was therefore established and the boy was closely monitored for pain relief and fluid intake. A strict input–output balance was maintained by the nurses, with the aim of maintaining a positive fluid balance. Regular pain relief with paracetamol and ibuprofen continued to be administered. Explanation and reassurance regarding the pain associated with the condition were regularly provided by nurses, who told the boy that it was of a temporary nature and usually resolved in a few days.
The boy was encouraged to continue gentle mobilisation in the bed, and physiotherapy assessment was planned for the following day, if necessary. Regular assessment of pain, along with monitoring of the Paediatric Early Warning Score (PEWS), was undertaken by the nurses. The patient remained comfortable and started to walk slowly the next day, reporting his pain levels to be 1 out of 10. His urine dipstick results remained normal, with no blood or myoglobinuria (risk of rhabdomyolysis).
On the third day of admission, further blood tests revealed a reducing CK level of 982 IU/litre. The boy was discharged later that day with explanation regarding red-flag manifestations (ie signs and symptoms that indicate the possible or probable presence of serious medical conditions that can cause significant morbidity or mortality, unless managed properly), such as a worsening of pain, loss of bowel or bladder control, swelling or discolouration of legs, high fever, and dark or brown-coloured urine. He remained well and was reviewed 6 weeks later in the PAU, when a repeat test to measure CK levels showed normal values at 59 IU/litre and aspartate transaminase of 21 IU/litre. He was discharged from hospital care.
Discussion
Overview of BACM
BACM was first described in the early 1900s as a complication of influenza infection by Leichtenstern (1905). In 1957, Lundberg published the first report of ‘myalgia cruris epidemica’, which appeared to be a newly identified syndrome of muscle pain, predominantly affecting the calf muscles, and occurring mainly in school-age children (Lundberg, 1957). The condition usually followed a prodrome (an early symptom indicating the onset of a disease) of febrile illness, typically seen in the early months of the year. It was predominantly reported in boys, many of whom had participated in strenuous activity before onset of pain. All children recovered within a week.
Lundberg felt that, in view of the well-described prodrome and the accumulation of cases within families and schools—in addition to leucopaenia and increased erythrocytic sedimentation rate demonstrated in affected patients—the aetiological agent was likely to be a virus (Lundberg, 1957). His work was followed by a cluster of scientific papers reporting the condition in the 1970s and 1980s (Buchta, 1977; Mejlszenkier et al, 1977; Antony et al, 1979; Ruff and Secrist, 1982; Zvolanek, 1984).
These typify the clinical presentation of BACM:
This condition generally affects school-age boys during viral epidemic seasons, which in most countries above the equator occurs between October and April (Ferrarini et al, 2014). It is associated with an isolated rise in CK and, when associated with other raised markers, this may denote a more serious pathology. Once diagnosed, BACM will spontaneously resolve with conservative management and requires monitoring to ensure quick recovery. It is therefore likely that awareness of this condition among all health professionals in an otherwise well child would reduce the need for invasive testing and admissions during epidemic periods due to its excellent self-limiting prognosis. As nurses are increasingly working in advanced roles such as paediatric ANP, as emergency nurse practitioners and practice nurses, they are directly involved in assessing and managing children. It is therefore important that they remain aware of BACM to make appropriate management plans and provide explanation and reassurance to the child and family.
Epidemiology
BACM mainly affects preschool-age children with a male predominance (≥80%) (Santos et al, 2014; Rosenberg et al, 2018). A 6-year study from Nebraska, USA, involving 5826 children showed a peak incidence of 2.6 per 100 000 during episodes of viral epidemic compared with 0.3 in non-epidemic periods (Buss et al, 2009).
There is also a strong correlation with the influenza type A or B virus, although other viruses have been linked with BACM. Those most likely to cause this syndrome are (Agyeman et al, 2004; Paul et al, 2017; Capoferri et al, 2018; Szenborn et al, 2018):
However, other organisms such as Toxoplasma and Mycoplasma pneumoniae have also been linked with the syndrome (Capoferri et al, 2018).
Current aetiological understanding of the viral post-drome is considered to be due to direct viral invasion into muscle fibres. This is supported by the available studies, where muscle biopsies demonstrated infiltration into the gastrocnemius and soleus muscles (Mejlszenkier et al, 1973; Ruff and Secrist, 1982).
Symptoms
Symptoms consist of gastrocnemius and soleus-muscle pain following a viral illness. The onset of pain tends to occur after a period of rest, ie on waking up. There is also a reduction in the range of movement and power. Neurological examination is reported as normal, and mild calf-muscle weakness is usually seen due to muscle pain rather than a true inability of muscle to generate power. Other non-specific symptoms, such as fever, headache, rhinorrhoea, vomiting and diarrhoea, may also be seen in some cases. The most common initial presentations as recorded in two large studies that involved a total of 354 children (Mackay et al, 1999; Agyeman et al, 2004) were:
It should be noted that acute onset lower limb-muscle pain without a rise in CK is unlikely to be due to BACM and may rather form a part of the myalgia associated with viral illnesses. It is therefore important to consider possible differential diagnoses, as presented in Table 1.
| Condition | Discernible presentation | Management |
|---|---|---|
| Non-accidental injury |
|
|
| Guillain-Barré syndrome |
|
Intravenous immunoglobulin therapy |
| Rhabdomyolysis (serious condition resulting from a direct or indirect muscle injury, causing death of muscle fibres and the release of their contents into the bloodstream) |
|
|
| Osteomyelitis |
|
Antibiotic therapy |
| Deep-vein thrombosis | Red, swollen leg, usually unilateral | Heparin and other supportive therapies |
| Juvenile rheumatoid arthritis |
|
If necessary: |
| Malignancy | Variable or non-specific presentations | Dependent on type of malignancy |
| Muscular dystrophy | Family history |
|
| Compartment syndrome | Pain out of proportion with a sensation of tightness around the limb, usually unilateral | Surgical reduction |
Investigations
Most children with BACM will have a solitary rise in CK. Studies have reported a wide range of CK values at admission:
This contrasts with viral-induced myositis, which does not have a concurrent increase in CK to such an elevated level (Paul et al, 2017). It is important to note that, where the diagnosis of BACM is clear in an otherwise well child, other investigations are not usually indicated. It is important that nurses highlight any newer onset of symptoms or detection of myoglobinuria (presence of myoglobin in the urine, usually associated with rhabdomyolysis or muscle destruction) because these may indicate an evolving serious pathology.
It is also important to note that there is no associated myoglobinuria. Muscle studies have been performed relatively infrequently in view of the short duration of symptoms and excellent prognosis. When electromyograms have been recorded, they have either been normal or suggestive of patchy myopathy changes (Neocleous et al, 2012). Few of the muscle biopsies taken in some earlier studies were reported as normal or found to demonstrate myositis, segmental rhabdomyolysis and moderate muscle necrosis with interstitial inflammation (Mejlszenkier et al, 1973; Ruff and Secrist, 1982).
An MRI scan may show increased weighting in the T2 image of the affected muscle, but again findings may differ. However, it may be a useful, non-invasive tool for the clinician to aid diagnosis of this condition where doubts regarding other serious pathologies may arise (Kawarai et al, 2007). In BACM, the pattern of abnormalities seen in an MRI signal differs from those seen in myositis of other causes. Abnormal signals in discrete portions of the affected muscles, with a sharp margin between areas of affected muscle and unaffected muscle, are seen on an MRI and are not associated with a mass or collection. Localised fascial and subcutaneous oedema may be seen in the tissues overlying the involved muscles (Panghaal et al, 2008).
Management
BACM is a self-limiting condition and requires supportive treatment. However, close monitoring of basic observations and PEWS, along with urine dipstick testing for differentials such as rhabdomyolysis, is necessary (Paul et al, 2017). To aid with walking, some gentle physiotherapy may be beneficial, as well as encouraging fluid intake to keep the child hydrated. An input/output chart may also help monitor the child's hydration status and prevent further complications. Serial CK levels may be a useful tool to monitor for a declining trend and eventual return to baseline to correlate with clinical improvement (Agyeman et al, 2004; Paul et al, 2017).
Prognosis
BACM is a self-limiting condition and prognosis is extremely good. A 4-year study of 54 children in two large tertiary paediatric hospitals based in Israel and Canada had a 100% safe discharge rate, with follow-up in paediatric clinics showing a drop in CK levels (Rosenberg et al, 2018). In another study from Hong Kong, carried out over a 10-year period with 71 children, no recurrence was reported, with overall good prognosis described (Sham and Tse, 2015). BACM is a self-limiting condition with few complications and has low levels of recurrence when followed up.
A recently published systematic literature review of sporadic BACM involving the calf muscles found that it is a self-limiting condition that can usually be diagnosed on a clinical basis and was never complicated by kidney involvement (Capoferri et al, 2018). The studies involved a total of 451 patients.
The nurse's role
Primary care and emergency department
Nurses and nurse practitioners working in primary care and the emergency department spend considerable time with children and their families. A potential diagnosis of BACM should be considered in seemingly well children with ongoing symptoms of calf-muscle pain, where there is no warmth or swelling but there is difficulty walking. The nurses, in addition to assessing the child and identifying the severity of the illness using PEWS, can highlight the possibility of BACM and, as part of providing holistic support to the family, they can ensure that unnecessary painful investigations are avoided. Their regular and prolonged contact with families puts them in an ideal position to act as the patient's advocate (McCabe et al, 2009).
Pain relief is vital for ensuring the child is as comfortable as possible and gentle mobilisation in the bed should be encouraged. It is important that an established pain scale is used to record objective assessment of the child's distress and pain, and to provide appropriate explanation and reassurance about the transient and temporary nature of BACM.
Paediatric ward
Children with BACM may be admitted to the children's ward for completion of investigations, supportive management and monitoring. Nurses play a vital role in ensuring that the child receives adequate analgesia and remains well hydrated, as well as encouraging the patient to remain gently mobile in bed for the initial 24 to 48 hours. Nurses will need to closely monitor children with BACM, repeat their vital observations at regular intervals and escalate any concerns if the PEWS is high. For BACM, in particular, regular observation of the urine colour and urinalysis are important to rule out the presence of myoglobinuria (tea-coloured urine with a positive urine dip test for blood), which is a potential sign of rhabdomyolysis (indicating ongoing muscle breakdown), because this can cause acute kidney injury and may result in the need for dialysis (Heiner et al, 2010).
Irrespective of their age, during a period of illness children tend to behave as if they are much younger and are often frightened of the attention and investigations focused on them. Nurses play a vital role in supporting families by providing them with appropriate information and reassurance, and also acting as an advocate for their concerns and expectations.
The role of the play specialist is vital and should be valued as part of the multidisciplinary team. Play specialists are able to prepare a child for a painful procedure, give information about their condition and treatment, provide emotional support or simply distract the young patient by playing a game or reading a story (Wilmot, 2007).
Conclusion
BACM is a self-limiting condition that predominantly affects boys during viral epidemic periods; it presents typically with a viral post-drome of calf pain in the absence of neurological findings or signs of inflammation. Early diagnosis through clinical suspicion, supported by an isolated elevated CK level in the blood tests, will help minimise invasive investigations. It is best managed conservatively with pain relief, observation and gentle remobilisation, which may require time and encouragement.
Follow-up attendance in clinic may be useful within a few weeks, with evidence of recovery expected. The prognosis is good and so the child should be expected to make a full recovery within a few weeks after being discharged.