Infection with nontuberculous mycobacteria should be considered when a
patient is seen with chronic, so-called sterile osteomyelitis and no other
infecting agent can be isolated. A high index of suspicion is necessary for
adequate diagnosis and treatment of this condition. In addition to cultures,
the use of polymerase chain reaction for mycobacteria may help to establish
the diagnosis. We present an unusual case of a patient who had chronic
osteomyelitis due to Mycobacterium chelonae that occurred after
arthroscopy of the knee. Our patient was informed that data concerning the
case would be submitted for publication.
Athirty-year-old woman presented with chronic exercise-induced pain as well
as night pain in the distal portion of the left thigh and in the left knee.
She reported intermittent swelling of the left knee and continuous weight loss
in the previous few months despite a normal appetite. The patient was being
treated with diclofenac for pain control. She reported a history of chronic
osteomyelitis that began when she was fifteen years of age, following
arthroscopy of the left knee to explore the possibility that a tear in the
medial meniscus was causing exercise-induced pain. The arthroscopic
exploration revealed hypertrophy of a plica, which was excised. Five days
after the operation, a fever developed along with effusion of the left knee
joint. Antibiotic treatment was started, but a dull pain in the left thigh
persisted. There were no radiographs or medical records available from that
time.
Over the following two years, the patient was treated six times with
surgical débridement of the distal part of the femur and different
antibiotic regimens, including gentamicin, various cephalosporins, penicillin,
and oxacillin. An infecting organism was never isolated. The diagnosis of
chronic osteomyelitis was established histologically and was confirmed at
subsequent operations.
Seven years after the initial diagnosis, nondraining chronic osteomyelitis
persisted and was treated with trepanation of the posterior cortex and
débridement of the distal portion of the femur with implantation of
gentamicin-impregnated polymethylmethacrylate beads. Despite these
interventions, the infection persisted and was associated with chronic pain,
elevated levels of C-reactive protein, and an elevated blood-sedimentation
rate. No other focus of infection could be identified. Because of persisting
pain in the left thigh, the patient presented for additional evaluation and
treatment.
Physical examination revealed no abnormalities except for scars on the
dorsal and lateral aspects of the left thigh. Neither sinus tracts nor other
signs of chronic drainage were seen. The gait was completely normal, and there
was no swelling or redness of the knee. Radiographs of the distal aspect of
the femur revealed diffuse sclerosis and a well-defined lucency with a
surrounding sclerotic margin, but no acute periosteal reaction
(Fig. 1). Magnetic resonance
imaging revealed a focus of chronic osteomyelitis in the central, distal
aspect of the femur and a pronounced perifocal edema. The central focus
appeared marked off in the manner of a localized inflammatory lesion
(Fig. 2). A second, smaller
lesion was identified in the medial condyle. A technetium-99m bone scan
revealed two areas with increased tracer uptake, corresponding to the
abnormalities on the magnetic resonance image
(Fig. 3). Additionally, a bone
scan with technetium-99m-labeled antigranulocyte antibodies demonstrated three
different areas with focal accumulation of antigranulocyte antibodies
(Fig. 4). The results of the
laboratory tests showed a normal white blood-cell count (8.9 ×
109/L) but revealed a slightly elevated erythrocyte sedimentation
rate (26 mm/hr) and an elevated C-reactive protein level (32.4 mg/L; normal
value, <5 mg/L).
Extensive débridement of the distal portion of the femur with
special focus on the three active sites was performed through lateral and
medial approaches. Biopsy specimens were taken from suspicious areas and were
sent for histological and microbiological workup. The medullary canal was
cleaned with use of a high-speed drill, the zones of sclerosis were resected,
and local jet lavage and irrigation with 3% hydrogen peroxide (volume per
volume) was performed. Bone defects were refilled with autogenous bone from
the iliac crest and with collagen sponges (Essex Pharma, Munich, Germany)
soaked with gentamicin and vancomycin. The incisions were closed primarily,
and two deep drains remained in place for two days. Postoperatively, the
patient was allowed to walk with tiptoe weight-bearing and was treated with
intravenous administration of cefuroxime (1.5 g, three times per day) and
clindamycin (300 mg, four times per day).
Gram-staining and Ziehl-Neelsen staining did not reveal microorganisms in
the removed tissue, and no microorganisms grew after prolonged incubation in
routine bacterial and fungal cultures. After six weeks, tissue cultures for
acid-fast bacilli demonstrated no growth. Histological analysis confirmed the
previous diagnosis of chronic osteomyelitis of the distal aspect of the femur
with a morphologically unspecific admixture of inflammatory cells, including
neutrophils, lymphocytes, and plasma cells next to fibrosis, bone destruction,
and new bone formation, but without the appearance of granulomas.
Bacterial DNA from the formalin-fixed, paraffin-embedded material was
extracted, and nested polymerase chain reaction was performed according to the
protocol of Cook et
al.1. Amplification
of the mycobacterial 65-kDa heat shock protein gene (Hsp 65) showed a specific
and intense signal of 133 base pairs. Subsequent restriction fragment analysis
with use of three different endonucleases showed a restriction pattern that
was specific for Mycobacterium chelonae
(Fig. 5). To verify this
result, the polymerase chain reaction product was sequenced. With use of the
Basic Local Alignment Search Tool (BLAST) program of the National Center for
Biotechnology Information (NCBI), United States National Institutes of Health
(NIH), a homology match was found, revealing a correspondence of 100% of the
analyzed base pairs with the Hsp 65 gene of Mycobacterium chelonae
(strain IP 140420006, accession AF07112 of the NCBI BLASTN database) and
thereby confirming the diagnosis of an infection with Mycobacterium
chelonae.
After the final microbiological result was confirmed, the previous
antibiotic therapy was discontinued and the patient was instead treated with
intravenous administration of amikacin (5 mg/kg body weight, two times per
day) and oral administration of co-trimoxazole (160 and 800 mg, two times per
day) and ciprofloxacin (500 mg, two times per day). Eleven days later, the
patient's hearing was noted to be impaired and the amikacin therapy was
discontinued. The patient continued to receive antibiotic therapy for one
year, during which time the hearing impairment resolved and the C-reactive
protein level normalized. The C-reactive protein level stayed in the normal
range after discontinuation of the antibiotic therapy. The patient walked with
tiptoe weight-bearing for twelve weeks. Full weight-bearing without pain was
achieved six months after the operation. At the two-year follow-up evaluation,
the patient was free of pain except for mild discomfort in the distal aspect
of the left thigh only after long and intense exercise, such as one hour of
running or two hours of cycling. The C-reactive protein level was in the
normal range (<0.5 mg/L) without antibiotics. Fluoride-18 positron emission
tomography revealed a substantial accumulation of radioactive tracer showing
elevated blood flow and ongoing bone rebuilding of the distal aspect of the
femur, and a bone scan with technetium-99m-labeled antigranulocyte antibodies
revealed only a moderate accumulation of granulocytes in the distal aspect of
the femur. The persistence of infection could be neither definitively
diagnosed nor excluded on the basis of these test results. Decades of
follow-up will be necessary to determine a truly final result of the
osteomyelitis in our patient, but the two-year success rate is very
encouraging.
Mycobacterium chelonae is a rapidly growing species in the
Mycobacterium fortuitum complex of atypical mycobacteria known to be
responsible for a distinct number of primary infections of the skin and soft
tissues2.
Osteomyelitis caused by this organism is rare and has been reported in only a
few patients; it has occurred principally in the sternum after cardiac
operations3,4
or in immunocompromised
patients5-8.
Sternal osteomyelitis is associated with a poor clinical prognosis, perhaps
related to late diagnosis and late onset of specific
treatment3.
Osteomyelitis that occurs in the femur of a healthy fifteen-year-old child is,
without doubt, an extremely rare occurrence.
In the case of our patient, histologically confirmed osteomyelitis
manifested itself in the distal aspect of the femur after arthroscopy of the
left knee. Exercise-induced pain without the discovery of an adequate
arthroscopic correlate may be explained by the presence of a preexisting
infection that was unrelated to the arthroscopy. Several operations followed
without isolation of an infecting organism. Surgical débridements and
antibiotic therapy were unsuccessful. In retrospect, it cannot be determined
whether Mycobacterium chelonae was present before the initial
arthroscopy, whether it was a complication of the arthroscopy, or whether it
was introduced at one of the subsequent débridements. However, no other
infectious organism was ever isolated. Furthermore, the persistence of
infection, despite multiple débridements and several different
antibiotic regimens, supports the primary diagnosis of osteomyelitis caused by
Mycobacterium chelonae.
Surgeons must take the initiative to request special microbiological
investigations to confirm the diagnosis when infection is suspected on the
basis of clinical and histological findings but routine cultures are reported
as negative. An awareness of fungi as well as nontuberculous mycobacteria is
the key to diagnosis and, consequently, to successful antibiotic treatment.
Although Mycobacterium chelonae is known to be a rapidly growing
bacterium, microbiological detection in classic culture assays is difficult
and often
unsuccessful9. In
addition, amplification of mycobacterial DNA with the use of polymerase chain
reaction has proven to be more sensitive than conventional detection
methods10.
Amplification of a portion of the highly conserved 65-kDa antigen of
mycobacteria, which encodes a heat shock protein with genus-specific epitopes,
permits the detection of not only the DNA of Mycobacterium
tuberculosis but also a wide variety of other mycobacterial species. In
addition, digestion of the polymerase chain reaction product with three
restriction enzymes followed by electrophoresis on agarose gel enables
distinction between Mycobacterium tuberculosis and atypical species
(and some atypical species from each other) because these species show
characteristic digestion patterns. Another method with which to subspecify the
detected mycobacterial DNA is sequencing the polymerase chain reaction product
and comparing the obtained nucleotide sequence with known sequences of several
mycobacterial species—for example, with use of the BLAST search program
of the National Center for Biotechnology Information, as mentioned above.
It therefore seems reasonable to perform both routine cultures and
polymerase chain reaction because antibiotic susceptibility studies can only
be performed in the classic culture assays. In the case of our patient,
treatment had to be started on the basis of the susceptibility results
published in the literature. Amikacin and ciprofloxacin have proven to be the
most effective antibiotics against microorganisms of the Mycobacterium
fortuitum complex, and sulfamethoxazole has also demonstrated a high rate
of
effectiveness2,3.
In general, treatment is recommended for at least six
months2,3.
In conclusion, this case demonstrates that fungi as well as the different
groups of mycobacteria should be suspected as causative agents when standard
microbiological techniques fail to identify the infecting agent in chronic
osteomyelitis. In addition to cultures, the highly sensitive polymerase chain
reaction for atypical mycobacteria should be performed in clinically
suspicious cases.