Focal Myositis-MRI

Case Report: 40 yr old male complaints  of  pain left  calf muscles  with  occasional fever and no hx of trauma, shows on MRI  enlargement/ oedema/ maintained fat planes  of tibialis anterior/ flexor digitorium longus/ both heads of gastrocnemius (medial>lateral) with no focal necrosis/ vascular  or skeletal abnormality, possibly representing focal myositis 

Teaching points by Dr MGK Murthy, MRI tech: Mr Ram Mohan

1. Focal myositis  is  a benign  inflammatory pseudo tumour  when it is not  part of the collagen disorders spectrum  including polymyositis. Clinically  may present with  non traumatic pain in  a muscle or groups of muscles of short duration with no significant systemic symptoms  or laboratory contribution(including viral markers and muscle enzymes/ leukocyte count etc) except possible increase in C-Reactive protein

2. X-rays  show no skeletal involvement  and Doppler excludes any vascular compromise. MRI is highly sensitive and specific with focal oedema  of concerned muscles  (type1- part of one muscle involved, type2 whole of one muscle , type 3 represents   a group of muscles in a compartment) with  enlargement (T1 low and T2/fat sat bright) , maintained inter muscular fat planes   with no bleed or vessels or skeletal abnormality 

3. Etiology could be  viral or denervation variety , with lower extremity predominance ( gastrocnemius/ vastus lateralis  / Adductors >others) with   no gender / age predilection. Three phase bone scan suggests focal calf muscle activity  with bone normal

4.Needle electromyography  may demonstrate possible denervation potentials.Usually self limiting and if need be, management with steroids / supportive therapy would  help, though may recur rarely