Una zoppia di difficile inquadramento diagnostico

We describe the symptoms in a girl, aged 12 years, who presented hip pain and we analyse the initial clinical picture and its worsening. It needs to be differentiated from septic arthritis, pyomyositis and transient synovitis among other disease. Septic hip should be the first diagnostic consideration in children with fever and acute hip pain. Pyomiositis should be considered if there is clinical suspicion of infection outside the hip joint. The patient represents an unusual case of pyomyositis of the psoas muscle caused by Group A beta-haemolytic streptococcus. Magnetic resonance is the preferred imaging modality for the diagnosis.