Mastoiditis secondary to mycobacterium abscessus imaged with gallium-67 scintigraphy
Department of Biomedical Imaging, University of Malaya, Kuala Lumpur, Malaysia
Atypical mycobacterium is rarely seen as a cause of
chronic mastoiditis but has been increasingly recognized over the past few
years. Mycobacterium abscessus is the most pathogenic and
chemotherapy-resistant, rapid-growing mycobacterium of all the four groups.
This paper presents a case of a 57-year-old woman who had chronic mastoiditis
with recurrent exacerbations. The initial computed tomography (CT) findings showed
the presence of an inflammatory process and she was treated with the
appropriate antibiotics. The patient subsequently underwent a tissue biopsy
when she presented with another exacerbation. At this time, the CT scan did not
identify the ongoing exacerbation, but the Gallium-67 scintigraphy did. � 2008
Biomedical Imaging and Intervention Journal. All rights reserved.
Keywords: Mastoiditis; Mycobacterium abscessus; gallium-67
Atypical mycobacterium is a rare entity implicated in de
novo mastoiditis. There are very few reported cases especially in the South-East
Asian region. Various strains of atypical mycobacterium have been known to
cause disease in human beings, since their isolation in the 1920s. Of the four
groups of atypical mycobacterium, the group IV rapid growers (Mycobacterium
abscessus and Mycobacterium fortuitum) are the ones which are
recognized as human pathogens .
This paper presents a case of a 57-year-old woman who had
chronic recurring mastoiditis and discusses the computed tomography (CT)
findings and the use of the Gallium-67 scintigraphy in this condition.
A 57-year-old woman, presented to the ENT clinic with
gradual loss of hearing and bilateral ear discharge. She also noticed that
pieces of bone were extruding from her left ear. She had been suffering from chronic
bilateral ear discharge since her early teenage years. The physical examination
done by the otorhinolaryngologist had shown some ear discharge, but there was no
evidence of abscess formation, nor was there any facial nerve palsy noted. A
presumptive diagnosis of bilateral chronic suppurative otitis media was made. Her
blood investigations were essentially normal apart from the normocytic
normochromic anemia. Ear swabs from the external auditory canal were sent for
microbiological analysis (culture and sensitivity) for pathogens, including Mycobacterium
A CT scan of the temporal bones revealed sclerosis of both
mastoid air cells with presence of soft tissue, bony erosion and bony fragments
within the external auditory canal (Figure 1 & 2). She was started on
treatment with oral co-trimoxazole because the initial clinical diagnosis prior
to the imaging studies was chronic suppurative otitis media. Her ear discharge
resolved and her hearing improved. The cultures were negative for pathogens,
including tuberculosis. After completing two months of oral antibiotics, she
began to notice discharge from her right ear. Due to the recurrent nature of
the infection, a tissue biopsy of the ear was performed and sent for culture
and sensitivity screening.
The tissue biopsy of the affected ear isolated a rapidly
growing atypical mycobacterium � Mycobacterium abscessus which was
resistant to co-trimoxazole (Bactrim) but sensitive to imipenem (intravenous
beta-lactam antibiotics), clarithromycin and azithromycin. She was commenced on
imipenem and clarithromycin. Intravenous amikacin was administered initially
for synergistic reasons but the patient was unable to tolerate amikacin and it
was withheld. This dual antibiotic regime was continued for a total of 40 days
without any complications.
A repeat CT scan of the temporal bone showed consolidation
of the previously inflamed bony lesions but was unable to give any information
on the activity of infection. A Gallium-67 (67Ga) scan was performed
and showed raised 67Ga uptake in the right petromastoid region
(Figures 3 and 4). The left petromastoid region showed near normal, but
slightly increased radiotracer uptake. This indicated the presence of active
infection and the need to continue treatment. ������
Upon completing the initial regime of antibiotics, she was
started on oral doxycycline 100mg bd, clarithromycin 500mg bd and moxifloxacin
400mg bd for life. She has been on regular follow up since then and has been
Mycobacteria are slow-growing aerobic, immobile bacilli
that have been identified by the property of acid-fastness. Atypical or
non-tuberculous Mycobacteria have been distinguished from the Mycobacterium
tuberculosis complex and classified into four groups by Runyon based on the
speed of growth, morphology and biochemical reactions . Atypical
mycobacteria are known to cause other clinical syndromes such as lymphadenitis
in children, lung and cutaneous infections in adults, and disseminated
infections in immunosuppressed patients. They are isolated and transmitted
through contaminated water. Geographically, outbreaks of atypical mycobacterial
infection have been reported especially in the Rocky Mountain territories of North America [1, 2].
Mycobacterium abscessus (previously known as M.
chelonae, subspecies abscessus) is a rare cause of chronic
mastoiditis, as less than 10 cases have been reported so far. According to
Redaelli de Zinis et al, there were only seven cases of otitis media
caused by Mycobacterium abscessus from 1976 to 2001 . Mycobacterium
abscessus is the most pathogenic and chemotherapy-resistant rapid-growing
mycobacteria commonly associated with penetrating trauma, surgery and the
presence of foreign bodies. It is also one of the mycobacteria that are most
often isolated from cystic fibrosis patients .
Infection caused by atypical mycobacterium in the
petro-mastoid region causes significant diagnostic and prognostic confusion. There
are no definite CT scan appearances to convince the clinician of the presence
of residual infection. At this juncture, it is of value to follow up such cases
with Gallium-67 (67Ga ) scintigraphy . From a clinical
standpoint, objective evidence of resolution of infection will help to guide
the management of these patients. It will allow the discontinuation of prolonged
antibiotic therapy, which may be expensive and potentially toxic.
The mechanism of 67Ga localization in inflamed
and infected tissue is believed to occur through three main processes. 67Ga
is carried bound to plasma transferrins to sites of inflammation and infection.
It is also retained within the intracellular lactoferrin of leucocytes which
will then migrate and accumulate at infection sites. Finally, 67Ga
itself may be bound to the siderophores produced by pathogenic organisms
localized at infection sites . It localizes very early and in relatively
high concentrations in the event of inflammation of the bony tissue. This makes
it the preferred technique for assessing resolution of infection and to
diagnose subclinical mastoiditis [4, 5]. The improvement or return to normal of
67Ga uptake at infection sites correlates well with the clinical
inactivity of the infection.
67Ga-citrate also accumulates in sites of
active bone remodeling but the intensity of uptake is relatively higher in the
presence of infection and it is less likely to persist following resolution of
infection. Thus used in combination, technetium-based agents and 67Ga
would be useful in both diagnosing as well as in the follow-up of these cases
In a study done by Strashun AM and colleagues in 1984, it
was found that clinically confirmed cases of otitis media were often
radiographically negative early in the course of the disease. However,
radionuclide scintigraphy with technetium and gallium radiopharmaceuticals,
have been demonstrated to be a more sensitive imaging modality . Although CT
is excellent for the localization and follow up of progression of soft tissue
in the petromastoid region, it cannot be used accurately in the follow up of
regression or inactivity of infection in this region . This is due to the
slow process of re-ossification in the skull bone.
CT is not significantly more sensitive (33%) than routine radiographic
techniques. Presumably this failure of early detection is due to the clinical
situation in which the inflammatory response, both soft tissue and bone, causes
severe and persistent ear pain that forces the patient to seek attention only
at the point in the disease where 30-50% of trabecular bone has been destroyed.
Additionally, the regional anatomy does not provide the
same advantages of earlier soft-tissue changes including swelling and
displacement of contiguous fat lines, swelling and obliteration of lucent
planes between muscles and subcutaneous edema, relied upon radiographically to
suggest the possibility of early long-bone osteomyelitis .
In this patient, the Mycobacterium abscessus
isolated was resistant to co-trimoxazole. It is important to note that the
patient was on a single therapy regimen for two weeks on this particular
antibiotic. This was because the initial working diagnosis was chronic
suppurative otitis media and co-trimoxazole is one of the antibiotics utilized
in this condition. Furthermore, the culture and sensitivity of the ear swabs
were not known at the initiation of therapy. Nevertheless, the initial
discharge had cleared with clinical improvement after two months of treatment.
It is likely that the Mycobacterium abscessus pathogen was initially
sensitive to co-trimoxazole, however, as it was only a mono-therapy, the
pathogen gradually developed resistance and the patient became symptomatic
Atypical rapidly-growing mycobacteria are resistant to
conventional antimycobacterial therapy, except aminoglycosides. New drugs such
as clarithromycin and erythromycin derivatives, with slightly greater activity
than the parent compound and fewer side effects than erythromycin, have proven
to be effective in treating M. chelonei infections . The role of life-long
antibiotic therapy is still under trial and is used at a few centres worldwide.
Figure 1 CT scan of temporal bone - Coronal reconstruction image showing soft tissue filling up the external auditory canal and the middle ear (long white arrows). There are also bony fragments seen (short black arrows).
Figure 2 CT of temporal bone - axial image, in bone window showing soft tissue filling up the external auditory canal and the middle ear (long white arrows). The bony fragments are clearly seen in this window. (short black arrows).
Figure 3 67Ga scintigraphy showing uptake in the right mastoid region. (black arrow).
Figure 4 SPECT 67Ga scintigraphy images showing significantly increased uptake in the right petromastoid region. (black arrow).
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|Received 3 January 2008; received in revised form 8 April 2008, accepted 28 April 2008
Correspondence: Department of Biomedical Imaging, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Malaysia. Tel.: +603-79492069; Fax: +603-79581973; E-mail: email@example.com (Anushya Vijayananthan).
Please cite as: Vijayananthan A, Arumugam AV, Kumar G, Harichandra D,
Mastoiditis secondary to mycobacterium abscessus imaged with gallium-67 scintigraphy, Biomed Imaging Interv J 2008; 4(2):e23