Forearmed and deceived: Diagnosis?

A 58-year-old male with a four-year history of noninsulin dependent diabetes presented in early January 1999 with a two-week history of progressive right fore arm swelling, pain, and limitation of wrist and elbow movement unassociated with recognized trauma. He had been febrile in the three days before the evaluation, despite having been on an anti-inflammatory medication for approximately one week. Progressive clinical worsening in association with a markedly elevated erythrocyte sedimentation rate prompted referral to an infectious diseases consultant regarding the possibility of osteomyelitis.

By the next day, the pa ti ent's blood cul tures were re ported positive for Staphy lo coc cus au reus, re sis tant to peni cil lin but sen si tive to oxacil lin. A bone scan showed dif fuse hy pere mia of the fore arm "con sis tent with an in flam ma tory con di tion such as cel lu li tis" and no evi dence of os teo mye li tis. The pa ti ent's an ti bi ot ics were changed to in tra ve nous clox acil lin. Over the next three days, the pa tient showed lit tle change in the ap pear ance or dis com fort of his arm de spite a decreas ing fe ver and de creas ing leu ko cy to sis.
A di ag nos tic pro ce dure was per formed. What is your di ag no sis?

DI AG NO SIS
A com put er ized ax ial to mo gram (CT) scan of the arm was obtained on the sixth day of hos pi tali za tion (Fig ure 1). It shows thick ening of the sub cu ta ne ous tis sue with an ex ten sive mul ti lo cu lated fluid col lec tion ex tend ing from the level of the wrist to the el bow, an te riorly and pos te ri orly through the in teros se ous space. Ad ja cent muscles ap peared swol len. The ra di olo gist's in ter pre ta tion was that it was mark edly ab nor mal with changes "in keep ing with dif fuse cel lu li tis, ab scess for ma tion and pos si ble myo si tis". An ul tra sono graphic exami na tion re vealed "a hy poechoic volar com part ment with loss of nor mal mus cle stria tion". The sono graphi cally ab nor mal area was aspi rated and a drain was in serted, re leas ing 40 mL of pu ru lent ma terial, which on Gram stain showed 4+ poly mor pho nu clear leu ko cytes and Gram-positive cocci in clus ters. The as pi rate yielded growth of S au reus with the same sen si tiv ity pat tern as the blood iso late. The patient was taken to the op er at ing room where co pi ous amounts of puru lent ma te rial were drained and the fore arm ir ri gated. All the mus cles were in tact, with no evi dence of ne cro tiz ing fas ci itis. A transtho racic echo car dio gram showed no ab nor mali ties. Post op eratively, the pa tient re ceived a to tal of four weeks of in tra ve nous and two weeks oral an ti mi cro bial ther apy, and made a slow but steady recov ery. Six months af ter sur gery, he had mild limi ta tion of pro na tion and supi na tion with re duced hand dex ter ity.

DIS CUS SION
De spite ad vances in the di ag no sis and ther apy of bac te rial dis ease, S au reus re mains a ma jor cause of soft tis sue in fec tion. These in fec tions can be ex tremely se ri ous, par ticu larly if as so ci ated with bac tere mia, where the over all mor tal ity has re mained un changed at 11% to 43% over the past 15 years (1). Dia betic pa tients, both in su lin and non in sulin de pend ent, ap pear to have a higher in ci dence of se vere and un usual in fec tions due to this or gan ism (2), as is seen in the pres ent case. Pos tulated mecha nisms for the lat ter in clude in creased colo ni za tion rates, abnor mal poly mor pho nu clear leu ko cyte func tion due to hy per gly ce mia, com ple ment dys func tion, and both macro-and micro vas cu lar changes (3).
This case also dem on strates the dif fi culty in clas si fy ing soft tis sue infec tions be cause their ex tent may only be as cer tained re lia bly by sur gical ex plo ra tion (4). Al though our case clearly was a deep space in fec tion, it is less clear whether it was a vari ant of pyo myo si tis or a non-necrotizing fas ci itis. Wall ing and Kaelin (5) de scribed 'non --tropical' pyo myo si tis oc cur ring in tem per ate coun tries and with an appar ent predi lec tion for pa tients with dia be tes mel li tus, where 56% of the in fec tions were caused by S au reus. The pa tho physi ol ogy of this entity may in volve the he ma toge nous seed ing of a trau matic in tra mus cular he matoma (6), with ini tial pain and mild swel ling fol lowed by 'woody' in du ra tion of the area. A sec ond phase with sys temic symptoms oc curs as iso lated pock ets of pu ru lent ma te rial de velop and a third, sep tic phase oc curs when en tire mus cle groups are re placed by pus. This case may have been an early phase of pyo myo si tis or a non inva sive form of fas ci itis with spread along fas cial planes. In cases of deep space in fec tions of the ex tremi ties where the ex act lo ca tion of the patho logi cal pro cess is un clear, a CT scan of the area may be a use ful radio logi cal mo dal ity. It may also aid in di rect ing a sur gi cal ap proach.