Acute osteomyelitis of the mandible caused by Rhodococcus equi in an immunocompromised patient: A case report and literature review
We present the first case of acute osteomyelitis of the mandible caused by Rhodococcus equi in an immunocompromised patient. A 53-year-old Caucasian man was referred to the outpatient clinic, because of a swelling of the left submental and submandibular spaces. The patient was immunocompromised owing to medication against myasthenia gravis and type II diabetes mellitus. The patient underwent surgical debridement under local anesthesia. Histologic examination showed acute osteomyelitis and both blood and pus cultures isolated Rhodococcus equi. The patient was discharged on linezolid 600 mg orally twice a day for 6 months and remains free of the disease 2 years postoperatively. Most patients with Rhodococcus infection are immunocompromised. Infection with this organism is rare and usually causes a distinct clinical syndrome resembling pulmonary tuberculosis. Diagnosis is frequently missed or delayed. Not only clinicians but also laboratory specialists should be aware of this organism, so as to contribute to prompt diagnosis and treatment of such infections.
Acute osteomyelitis of the mandible caused by Rhodococcus equi in
an immunocompromised patient: a case report and literature
George Rallis, MD, DDS, PhD,
Panayotis Dais, MD, DDS,
George Gkinis, MD, DDS,
Constantinos Mourouzis, MD, DDS, PhD,
Vasiliki Papaioannou, MD,
and Michael Mezitis, DDS,
GENERAL HOSPITAL OF ATTICA “KAT”
We present the ﬁrst case of acute osteomyelitis of the mandible caused by Rhodococcus equi in an
immunocompromised patient. A 53-year-old Caucasian man was referred to the outpatient clinic, because of a swelling of
the left submental and submandibular spaces. The patient was immunocompromised owing to medication against myasthenia
gravis and type II diabetes mellitus.
The patient underwent surgical debridement under local anesthesia. Histologic examination showed acute
osteomyelitis and both blood and pus cultures isolated Rhodococcus equi. The patient was discharged on linezolid 600 mg
orally twice a day for 6 months and remains free of the disease 2 years postoperatively. Most patients with Rhodococcus
infection are immunocompromised. Infection with this organism is rare and usually causes a distinct clinical syndrome
resembling pulmonary tuberculosis. Diagnosis is frequently missed or delayed. Not only clinicians but also laboratory
specialists should be aware of this organism, so as to contribute to prompt diagnosis and treatment of such infections. (Oral
Surg Oral Med Oral Pathol Oral Radiol 2012;114:e1-e5)
Rhodococcus is a facultative anaerobic, intracellular,
nonmotile, non–spore-forming, gram-positive coccoba-
cillus. Called Rhodococcus because of the ability to
form a red (salmon-colored) pigment, it can be weakly
acid-fast and bears a similarity to diphtheroids.
Rhodococcus was ﬁrst isolated in 1923 by Magnus-
son from lung abscesses in foals.
tion in humans was ﬁrst reported in 1967 in a patient
with plasma cell hepatitis receiving steroid therapy.
Since then, Rhodococcus has become an important op-
portunistic pathogen in immunocompromised patients,
especially those with acquired immune deﬁciency syn-
drome (AIDS), with the ﬁrst case in a patient with
AIDS being published in 1986.
This organism most
commonly produces a clinical syndrome involving the
lungs; however, osteomyelitis and abscesses in other
organs have also been reported.
The ﬁrst case of osteomyelitis of the mandible
caused by Rhodococcus in an immunocompromised
patient is described, and the difﬁculties in diagnosis as
well as the proper management are discussed.
A 53-year-old white male was referred to the outpatient
clinic by his family physician with a 4-week history of tender
swelling in left submental and submandibular areas. There
was redness on the skin without any sign of ﬂuctuation. The
patient was febrile with a temperature of 39°C. On intraoral
examination, there was no sign of infection and the vitality of
the teeth was normal. An orthopantogram (OPG) was ob-
tained and showed diffuse erosion on the inferior border of
the left mandible without any sign of possible odontogenic
infection (Figure 1). The patient denied any trauma to the
affected area. Medical history was remarkable for myasthenia
gravis under treatment with azathioprine, prednisone, and
pyridostigmine, and also diabetes mellitus as a complication
of prednisone therapy (on metformin). Two months before the
neck swelling, admission to the intensive care unit (ICU) for
pneumonia was reported. The patient also mentioned that
because of this history of pneumonia, the family physician
had ordered a computed tomography (CT) scan of the thorax,
along with magnetic resonance imaging (MRI) of the right
lower limb, owing to a coexisting swelling of the patient’s
right thigh. The most remarkable CT ﬁndings were a left
pleural effusion and a heterogeneous lesion of the left axilla
(Figure 2). The MRI revealed a lesion measuring 8 ⫻ 4cmat
Oral and Maxillofacial Surgeon, Head, Department of Oral & Max-
illofacial Surgery, General Hospital of Attica “KAT”, Athens,
Trainee in Oral and Maxillofacial Surgery, Department of Oral &
Maxillofacial Surgery, General Hospital of Attica “KAT”, Athens,
Oral and Maxillofacial Surgeon, Specialist, Department of Oral &
Maxillofacial Surgery, General Hospital of Attica “KAT”, Athens,
Microbiologist Specialist Microbiology Department, General Hos-
pital of Attica “KAT”, Athens, Greece.
Oral and Maxillofacial Surgeon, Director, Department of Oral &
Maxillofacial Surgery, General Hospital of Attica “KAT”, Athens,
Received for publication Aug 20, 2011; accepted for publication Sep
© 2012 Elsevier Inc. All rights reserved.
2212-4403/$ - see front matter
Vol. 114 No. 4 October 2012
the lower part of the lateral vastus muscle, with thick walls,
which was reinforced after intravenous gadolinium, and was
compatible to an abscess (Figure 3).
On admission, the patient had a leukocyte count of 12,700
cells/mL with 84% neutrophils, along with elevated erythro-
cyte sedimentation rate and C-reactive protein values, 106
mm/h and 15 mg/dL, respectively. The patient was initially
placed on ampicillin/sulbactam and metronidazole intrave-
A decision was made for multiple blood cultures, ultra-
sound scan (U/S) and ﬁne needle aspiration (FNA) of the
swelling. The U/S demonstrated inﬂammation and enlarged
lymph nodes, without any pus collection. The FNA cytology
showed inﬂammatory cells, mostly polymorphonuclear cells,
without any malignant cells. On the second day, there was no
clinical improvement and a CT scan of the mandible and the
neck was ordered. The CT scan revealed a heterogeneous
lesion of the left submental and submandibular areas, multiple
cervical lymph nodes, and erosion on the inferior border of
the left mandibular body (Figures 4 and 5). The lesion was
similar in appearance to the lesion revealed in the left axilla.
The differential diagnosis included infections of speciﬁc
and nonspeciﬁc etiology and neoplasms. Human immunode-
ﬁciency virus (HIV) and Mantoux tests were negative.
Based on the CT scan ﬁndings, an open biopsy was de-
cided. Pus swab was sent for culture and sensitivity, and
specimens from both the soft tissue and the bone were sent for
histologic examinations. Intraoperatively, there was strong
clinical evidence of active osteomyelitis, and there was de-
struction of the buccal cortex of the inferior border of the
mandible. The affected area was thoroughly debrided and
irrigated (Figure 6).
Both blood and pus cultures, after 6 days of incubation,
grew Rhodococcus equi through a CAMP test (API Coryne/
bioMérieux, La Balme les Grottes, France) (Figures 7 and 8).
The patient was then placed on meropenem and vancomy-
cin intravenously for 3 weeks, based on the sensitivity tests,
and ﬁnally defervesced on the 12th day after admission, 3
days after targeted intravenous medication was started. The
histology features of the lesion were consistent with osteo-
myelitis. The patient was discharged on the 30th day, and
continued on linezolid 600 mg orally twice a day for 6
months, according to the recommendation of the infectious
disease specialist. A new CT scan of the neck, mandible, and
thorax and an MRI of the right lower limb at 7 months
Fig. 1. OPG on admission showing erosion on the inferior
border of the left mandibular body (arrow).
Fig. 2. CT scan of the thorax showing heterogeneous lesion
of left axilla (arrow).
Fig. 3. MRI scan of the right thigh (coronal view) demon-
strating an intramuscular abscess (arrow).
Fig. 4. CT scan of the neck showing heterogeneous lesion of
left submental and submandibular spaces (arrow).
ORAL AND MAXILLOFACIAL SURGERY OOOO
e2 Rallis et al. October 2012
showed no active osteomyelitis and complete resolution of all
lesions, while the patient remains in good physical condition
2 years postoperatively (Figure 9).
The genus Rhodococcus primarily causes zoonotic in-
fections, and contains 42 species, with R. equi being the
most important human pathogen.
The other human
pathogens, R. erythropolis, R. rhodnii, and R. rhodo-
chrous, are rarely recovered from clinical specimens,
although R. erythropolis has recently been identiﬁed as
part of the regional microﬂora of individuals with nor-
mal and dry eyes.
The natural habitat of Rhodococcus is soil contami-
nated with animal manure, with infection being ac-
quired by inhalation, inoculation, or ingestion, perhaps
accounting for infection in persons who do not recall
contact with animals.
Rhodococcus affects individuals of all ages. Most
patients are immunocompromised, primarily those with
defects in cell-mediated immunity by HIV infection,
malignancy, or medications.
After the ﬁrst case re-
ported in a human in 1967, there have been more than
200 cases in the literature, mostly in immunocompro-
mised patients, especially HIV-positive patients, and
transplant recipients. Only 10% of the cases were in
In adults, the organism has been the etiologic agent
in pneumonia, pulmonary cavitation, pleural effusion,
bacteremia, osteomyelitis, and abscesses.
the best of our knowledge, only 5 cases of osteomyelitis
owing to Rhodococcus infection have been published
The lung is the most common site of infection. Onset
of the illness is usually insidious and the disease is
characteristically slowly progressive. From the lungs,
the organism can spread hematogenously, resulting in
Fig. 5. CT scan of the neck (bony window) demonstrating an
erosion of left mandibular body (arrow).
Fig. 6. Postoperative OPG.
Fig. 7. Rhodococcus colonies after 6 days of incubation.
Fig. 8. CAMP test.
Fig. 9. Clinical photo of the patient 2 years postoperatively.
OOOO CASE REPORT
Volume 114, Number 4 Rallis et al. e3
abscesses in other organs. In patients with AIDS, the
initial presentation may be confused with Pneumocystis
Symptoms, course, and response to therapy differ
signiﬁcantly between immunocompromised and immu-
nocompetent hosts, with the former usually presenting
with necrotizing pneumonia, having a high mortality
rate, and requiring prolonged treatment with a combi-
nation of antibiotics. Immunocompetent hosts, mostly
children, present with extrapulmonary lesions, a lower
mortality rate, and respond to a shorter period of treat-
ment, usually with a single antibiotic.
The diagnosis is usually delayed, because Rhodococ-
cus can easily be misconstrued as typical or atypical
mycobacteria, owing to insidious onset, chronic course,
involvement of the lung with cavitation, granuloma
formation, acid-fast staining characteristics, and growth
on Löwenstein-Jensen cultures. It can also be mistaken
for a diphtheroid and be discarded as a contaminant
however, blood cultures from severely immunocom-
promised patients with R. equi infection often contain
the organism. Patients’ blood cultures may be positive
in 65% of cases secondary to HIV infection.
Cellular immunity is important in protection against
inoculation. Rhodococcus is an intracellular organism
and survives in macrophages.
Thus, antibiotics that
penetrate neutrophils may be effective. In adults, recur-
rent disease appears to be common.
In the cases thus far reported in the literature, com-
bination therapy for 2 to 6 months appears to be most
successful. Surgical intervention, whenever possible,
increases probability of deﬁnite cure.
In general, the prognosis of Rhodococcus infec-
tions depends on the underlying immunosuppressive
conditions and other concurrent infections. Overall
mortality rate reaches 25%, although patients with
AIDS with documented R. equi pneumonia can have
higher than 50% mortality and a clinical course
punctuated by multiple relapses; the latter are com-
mon even when appropriate treatment is ultimately
Early diagnosis and treatment may prevent
chronicity and relapses. Prognosis is favorable in
most local Rhodococcus infections and among im-
Our case was an osteomyelitis of the mandible in an
immunocompromised patient. We could assume that os-
teomyelitis was an extrapulmonary site lesion, as the
patient was admitted to the ICU because of pneumonia a
couple of months earlier. The exact route of infection
could not be identiﬁed, however, as the patient did not
suffer active pulmonary infection by the time of admis-
sion. In addition, during hospitalization in the ICU, Rho-
dococcus was never isolated from the respiratory tract,
or from blood cultures. Nevertheless, the simultaneous
complete remission of the coexistent lesions in the
mandible, axilla, and right femur after antibiotic ther-
apy could lead us to the probable conclusion that they
all were extrapulmonary lesions originating from that
pneumonia, attributable to the same microorganism.
Unfortunately, specimens from the concurrent lesions
in the left axilla and right thigh could not be retrieved,
owing to the patient’s poor cooperation. The above
hypotheses are in accordance to the multifocal nature of
the infectious disease, presenting with multiple ab-
scesses in other organs.
To the best of our knowledge, the present patient
represents the ﬁrst case of osteomyelitis of the mandi-
ble attributable to R. equi. Combination antibiotic ther-
apy was administered along with surgical intervention,
offering the patient deﬁnite cure, which is in agreement
with the international literature.
A high index of suspicion is necessary for early
diagnosis of Rhodococcus infections. Medical pitfalls
are mainly because of delayed diagnosis. Increased
awareness on the part of both clinicians and laborato-
rians is needed for timely diagnosis and treatment of
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Table I. Cases of osteomyelitis caused by Rhodococcus
Author (year) Immunocompromised Site of infection Species
Broughton et al.
(1981) No Left hand thumb and index ﬁnger,
left foot third toe, right knee
Novak et al.
(1988) Yes Metaphysis of left femur R. equi
Fischer et al.
(1998) Yes Thoracic vertebra R. equi
Sistla et al.
(2009) No Right hip joint R. equi
Roy et al.
(2009) No Toe R. erythropolis
Present case (2011) Yes Mandible R. equi
ORAL AND MAXILLOFACIAL SURGERY OOOO
e4 Rallis et al. October 2012
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Panayotis Dais, MD, DDS
Department of Oral & Maxillofacial Surgery
General Hospital of Attica “KAT”
21, Dimokratias Street
Kiato, 202 00 Greece
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