benign acute childhood myositis ( bacm ) is a self - limiting process characterized by sudden onset of muscle pain , more often calf pain , manifested by walking difficulty . since many clinicians are not familiar with bacm , it is often misdiagnosed and interpreted as a more severe and complex disease . we report the case of a patient suffering from bacm in absence of any previous documented viral infections . we underline how medical history and clinical examination are sufficient for a correct diagnosis of bacm , as well as to avoid unnecessary tests . based on the previous reports , we updated etiology and clinical data of bacm , and we propose differential diagnosis of muscle pain in children . a 7-year - old boy with acute calf pain and progressive walking difficulty was referred to our pediatric center to rule out muscle degenerative diseases . two days earlier the child had suffered from fever , cough , malaise and rhinorrhea , which promptly resolved . the onset of calf pain was early in the morning , and it was so sharp that he had to walk on his heels mimicking a spastic gait . the child had undergone all compulsory vaccinations , and his previous clinical history was not suggestive of any remarkable diseases . no travels , trauma , vigorous exercise or similar episodes of limb pain were reported before onset of symptoms . on admission , reflexes and sensitivity of the upper and lower limbs were also normal . at rest , the patient kept his feet in slight plantar flexion . gastrocnemius - soleus muscles on both sides were soft on palpation , and there were no inflammatory changes . passive dorsiflexion of the ankles caused sharp pain as well as passive stretching and gentle palpation of his calves . despite normal neurological examination , the patient was hospitalized in order to allow medical observation and exclude severe diseases . on admission laboratory tests showed a significant increase in blood levels of creatinine phosphokinase ( 2161 u / l , normal range < 227 u / l ) , alanine transaminase ( 69 u / l , normal range : 0 - 45 ) and aspartate transaminase ( 92 u / l , normal range : 17 - 59 ) . mg / l ) and white blood cell count ( 7400/l ) were within normal limits . complete blood count , electrolytes , blood urea nitrogen , creatinine , prothrombin time , partial thromboplastin time and other routine blood parameters were also within normal limits . furthermore , serological tests ruled out recent viral infections by adenovirus , respiratory syncytial virus , cytomegalovirus , herpes virus and epstein  barr virus , as well as serological tests for mycoplasma pneumonia . since the patient refused to eat and drink , he received intravenous hydration for 24 h. during the 2 day of hospitalization pain spontaneously resolved and a normal gait was regained . considering that daily urine output was normal , the boy was discharged , and no long - term follow - up was required . benign acute childhood myositis is a self - limiting process which frequently affects the gastrocnemius and soleus muscles . in a review of 2004 other agents such as enterovirus , mycoplasma pneumonia and dengue virus have been involved in the process . furthermore , five cases of bacm following h1n1 influenza a virus infection and human parainfluenza virus type 1 infection have been reported . in most cases , the disease is self - limiting and when the myositis develops the patient is already in the early convalescent phase of the viral illness . nevertheless , it is reported that 10/316 children ( 3% ) developed severe rhabdomyolysis , and temporary dialysis was necessary in six cases . during winter 20072008 , influenza b virus was responsible for a large number of cases of bacm in germany , especially among male children aged from 6 to 9 years . median time between the onset of fever and the beginning of bacm symptoms was 3 days . despite the clinical course of bacm being well described , mall et al . furthermore , the exact current incidence , prevalence and pathogenesis of bacm are not known . this could simply be explained by the increased tropism of viruses for immature muscle cells . furthermore , each virus could act as a trigger in genetically predisposed children and in few patients with undiagnosed metabolic diseases . nevertheless , the onset may be mistaken for very severe neurological illness such as guillain  barr syndrome or chronic autoimmune diseases . as a consequence unnecessary invasive tests , such as radiography , echocardiography , daily medical examination and urine dipstick ( with measurement of myoglobin ) are sufficient to promptly detect complications and rule out more severe illnesses and creatine kinase ( ck ) should be measured only at diagnosis in order to early exclude degenerative diseases . viral tests for bacm - related viruses should not be routinely performed because of the time interval between infection and seroconversion . moreover , not always etiological agents can be found , and antiviral drugs are not usually recommended . nevertheless , influenza test may be useful since influenza viruses can affect the severity of bacm . however , parents should be encouraged to monitor the child 's urine output and the appearance of coca - cola colored urine and swollen legs . hospitalization should be scheduled only when the patient 's parents do not seem able to monitor the condition of their child at home . we report signs and symptoms which can help clinicians to make a correct differential diagnosis when a child suffers from acute muscle pain in table 1 . . a family history of neuromuscular disorders , myoglobinuria , trauma , chronic progression , rash , edema , muscle weakness or neurological diseases are not typically associated to bacm ; in these cases further investigation is required .
acute muscle pain and walking difficulty are symptoms compatible with both benign and severe degenerative diseases . as a consequence , in some cases 
 invasive tests and hospitalizations are improperly scheduled . 
 we report the case of a 7-year - old child suffering from acute calf pain and abnormal gait following flu - like symptoms 
 . a review of the literature will be helpful to better define differential diagnosis in cases of muscle pain in children . 
 daily physical examination and urine dipstick are sufficient to confirm the diagnosis of benign acute childhood myositis ( bacm ) during the acute phase , to promptly detect severe complications and to rule out degenerative diseases 
 . children with bacm do not require hospitalization , medical interventions or long - term follow - up .