focal myositis is an idiopathic inflammatory myopathy and a rare inflammatory pseudotumor of the skeletal muscle with unknown etiology ( 1 ) . the disease typically disappears spontaneously , does not last more than 4 years , and has no recurrence ( 1,2 ) . this myositis can be treated successfully with steroids or nonsteroidal anti - inflammatory drugs ( nsaids ) ( 1,2 ) . we herein describe the case of a man with recurrent episodes of bilateral focal myositis . a 38-year - old man presented with myalgia of the right gastrocnemius muscle in may 2005 . a needle biopsy of the muscle was performed in another hospital and indicated no malignancy . the patient did not receive any treatment at this time . as his symptom did not improve , he visited our hospital in august 2005 with tenderness of the right gastrocnemius muscle . on physical examination , no significant signs were detected on the skin , cardiovascular , respiratory , or abdominal examinations . manual muscle testing indicated full scores except in the right gastrocnemius , which demonstrated grade 4 ( of 5 ) because of myalgia . evaluations of his mental status , sensory , and cerebellar systems were normal . laboratory data indicated that the patient 's serum creatine kinase ( ck ) , aldolase , myoglobin , erythrocyte sedimentation rate ( esr ) , and c - reactive protein ( crp ) were within normal limits , and anti - jo-1 autoantibody , anti - ars autoantibody , and antinuclear antibody were negative ( table ) . hepatitis b surface antigen ( hbs ag ) was positive ( cut - off > 2,000 ) , and hb virus dna was negative ( < 3.7 leg / ml ) . human immunodeficiency virus ( hiv ) and hepatitis c virus antibody tests were negative ( table ) . magnetic resonance imaging ( mri ) revealed very high signal intensity in the right gastrocnemius medial head muscle on a short - tau inversion recovery ( stir ) image . 1a and b ) . a muscle biopsy of the right gastrocnemius revealed interstitial muscle infiltration by mononuclear inflammatory cells without findings of vasculitis , along with muscle fiber necrosis and regeneration ( fig . 2a and b ) . immunohistochemical staining of the muscle biopsy showed that the infiltrating cells predominantly consisted of cd4 + t cells , cd68 + macrophages , and cd20 + b cells accompanied by a few cd8 + t cells ( fig . focal myositis was diagnosed . magnetic resonance imaging ( mri ) of the lower limbs . a , b : august 2005 ; c , d , e : june 2006 ; f , g , h : january 2008 . a , b , e , f , h : axial ( a , f ) and coronal ( b , e , h ) . a - f : unenhanced mri image and g : gadolinium - enhanced mri image . stir images show high signal intensity in the affected muscles of the lower legs ( white arrowhead ) . c , d : axial and coronal stir images show high signal intensity in the affected femoral muscles ( white arrowhead ) . f , g : axial gadolinium - enhanced mri ( g ) shows no enhanced area in the thickened fascia of the right gastrocnemius , which showed high signal intensity on the unenhanced mri image ( f ) ( white arrow ) . muscle biopsy . a , b : hematoxylin and eosin staining , 400 ; c - f : immunohistochemical staining , 400 ; c : cd4 ; d : cd8 ; e : cd68 ; f : cd20 ; g : electron microscopy . a muscle biopsy of the right gastrocnemius reveals mononuclear inflammatory cells ( a , b : black arrowhead ) that infiltrated the interstitial spaces of the muscle without vasculitis findings , along with muscle fiber necrosis and regeneration ( a , b : white arrowhead ) . infiltrating cells predominantly consisted of cd4+t cells , cd68+macrophages , and cd20+b cells accompanied by a few cd8+t cells ( c - f : white arrow ) . electron microscopy of the muscle biopsy specimens reveals nemaline rods ( g : black arrows ) . as the patient was hbs ag - positive , lamivudine treatment was initiated for the prevention of de novo hepatitis under immunosuppressive conditions . prednisolone ( psl ) ( 30 mg / day ) was administered to treat the focal myositis in september 2005 , and his symptoms and mri findings were immediately improved . the clinical course is shown in fig . the patient 's muscle pain worsened gradually at around this time , and walking became difficult without a cane in june 2006 . although his crp level was 0.4 mg / dl , the serum myogenic enzyme level was not re - elevated . mri revealed multiple high - intensity areas in the lower limbs that included the femoral muscle ( both sides of the vastus lateralis , the left vastus intermedius , the right biceps femoris , and the left gracilis ) ( fig . the psl dosage was increased to 60 mg / day for relapse of myositis , and the patient 's symptoms immediately improved . psl : prednisolone , mtx : methotrexate , aza : azathioprine , ivig : high - dose intravenous immunoglobulin after tapering the psl dosage to 17.5 mg / day , a second myositis relapse occurred in october 2007 . 1f and h ) , left popliteus muscle , and right semimembranosus on stir images ( data not shown ) , and mild edema was evident in the subcutaneous tissue in both lower limbs in january 2008 . as thickening of the fascia of the right gastrocnemius on the stir image ( fig . 1 g , white arrow ) , it was considered to result from edema . because the patient was unusually resistant to the treatment for focal myositis , we performed a muscle biopsy of the left gastrocnemius to re - confirm the diagnosis , which showed a similar result to the first biopsy ( data not shown ) . electron microscopy of the muscle biopsy specimens in february 2008 revealed nemaline rods ( fig . the dosage of psl was again increased to 60 mg / day for the third relapse of myositis . thereafter , we administered azathioprine ( max 100 mg / day ) for a steroid - sparing effect , but it failed to bring the patient persistent relief from his myalgia and gait disturbance . therefore , we were forced to continue to administer 15 mg / day or more of the steroid in order to maintain remission . in september 2011 , the relapse of myositis involved myalgia of both lower limbs and arthralgia of both foot joints . the patient 's psl dosage was increased from 15 mg / day to 30 mg / day , however , the effect was incomplete . as he had a compression fracture of the vertebrae due to steroid - induced osteoporosis , high - dosage psl treatment was avoided . methotrexate ( mtx ) ( 7.5 mg / week ) was initiated with psl 20 mg / day in october 2011 , as hepatitis b virus ( hbv ) infection had been controlled by lamivudine . the dosage of mtx was gradually increased to 16 mg / week by august 2012 . . the patient can maintain standing on his heels , but not on his tiptoes . the differential diagnoses of inflammatory myopathy were postulated to be polymyositis , dermatomyositis , inclusion body myositis , eosinophilic myositis , and sarcoidosis . he had no past medical history and no other organ disorders including those affecting the skin and lung . the lesion originated from the distal muscle , with no eosinophilia or increase of ck or crp in the peripheral blood . the pathology of the muscle biopsy revealed myositis and did not indicate granulomas , eosinophilic infiltration , or vacuoles . focal myositis is a type v idiopathic inflammatory myopathy , classified by bohan and peter as miscellaneous myopathies ( 3 ) . the levels of acute phase reactants and myogenic enzymes , such as ck , and the site of the involved muscle also vary in myositis ( 1,2,4 - 10 ) . in this case , the patient 's myalgia began in the right gastrocnemius and spread to both lower limbs . morevoer , sekiguchi et al . reported that normal serum crp and ck levels might be associated with mild muscle inflammation in patients with focal myositis ( 11 ) . although the mechanism of muscle pain is not fully understood , inflammatory muscle pain was related to molecules including interleukin ( il)-6 , tumor necrosis factor - alpha , il-1beta , and kinin in experiments using animal models ( 12,13 ) . dina et al . reported a novel experimental model of chronic muscle pain induced by mild acute muscle inflammation ( 14 ) . psl is presumed to have led to the alleviation of symptoms by suppressing muscle inflammation . some reports have reported an association between chronic hbv infection and myositis ( 15 - 17 ) . lamivudine or entecavir , antiviral therapies for hbv infection , improved symptoms in patients with myositis ( 18,19 ) . reported that the investigation of possible viral etiology via polymerase chain reaction was negative in focal myositis ( 20 ) . the present patient was an hbv carrier , however , antiviral therapy did not affect his myositis . although electron microscopy of specimens from the second muscle biopsy revealed nemaline rods , we judged the finding to be a non - specific change because his clinical syndrome was not characteristic of nemaline myopathy ( 24 ) , and there have been several reports concerning the non - specific finding of nemaline rods in inflammatory myopathies ( polymyositis and dermatomyositis ) ( 22 - 25 ) . the majority of focal myositis cases involve a limited lesion , and bilateral lesions are rare . in our case , the patient demonstrated myositis progression from the right gastrocnemius to both sides approximately 1 year after onset and recurrent myalgia , and the myositis had temporary femoral muscle involvement . heffner jr et al . reported six patients with polymyositis beginning as a focal process that rapidly progressed 3 - 6 months from the onset , and some cases of bilateral focal myositis have been reported ( 26 ) . additionally , some reports have discussed the difference between focal myositis and polymyositis ( 27,28 ) . conversely , there are also some reports of polymyositis cases with distal muscle involvement or without elevation of serum ck ( 29 - 34 ) . the muscle biopsy in our case showed mononuclear inflammatory infiltrates that predominantly consisted of cd4 + t cells . previous studies also reported cd4 + -dominant cell infiltration in the muscle in focal myositis ( 37,38 ) and dermatomyositis ( 35,36 ) , but not in polymyositis ( 39 ) . in our patient , muscle weakness derived from myalgia was present but not progressive , and his immunohistochemical findings indicated focal myositis rather than polymyositis . it appears that focal myositis and polymyositis have different pathophysiological mechanisms ; however , whether focal myositis is a subtype of polymyositis remains to be determined . focal myositis usually shows a good response to treatment with psl and nsaids ( 2 ) . it has a good prognosis and might be a self - limiting disease ( 1 - 3 ) . furthermore , the response to nsaids is often good even in cases of repeated relapse ( 41 - 43 ) , and some cases of spontaneous remission have occurred ( 8,49 ) . although the present patient demonstrated a good response to steroid treatment , psl dose reduction induced the recurrence of myalgia . because he experienced repeated myositis relapses when the psl dose was reduced to 15 - 17.5 mg , it became necessary to use immunosuppressive agents for a steroid - sparing effect . azathioprine and ivig did not affect the patient 's myositis . because his hbv infection was successfully controlled with lamivudine , we used mtx and were able to reduce the psl dose . reports of immunosuppressive therapy for focal myositis are limited ( 6,47,51,52 ) , and only one previous case report , in a child , described mtx treatment for this condition ( 47 ) . further studies are needed in order to clarify the sparing effect of treatment via mtx in steroid - resistant cases of focal myositis .
this report describes a rare case of recurrent bilateral focal myositis and its successful treatment via methotrexate . 
 a 38-year - old man presented myalgia of the right gastrocnemius in may 2005 . 
 magnetic resonance imaging showed very high signal intensity in the right gastrocnemius on short - tau inversion recovery images . 
 a muscle biopsy revealed inflammatory cd4 + cell - dominant myogenic change . 
 focal myositis was diagnosed . 
 the first steroid treatment was effective . 
 tapering of prednisolone , however , repeatedly induced myositis relapse , which progressed to multiple muscle lesions of both lower limbs . 
 initiation of methotrexate finally allowed successful tapering of prednisolone , with no relapse in the past 4 years .