Joint Program in Nuclear Medicine
Septic Sacro-Ilitis in an IV Drug User
Gail P. Sorrel, MD
No date
Presentation
A 39 year-old male with a 16 year history of IV drug use presented
to the ER with a four day history of intense left buttock pain
which radiated down his left leg posteriorly. He complained also
of fever and night sweats. The pain would awaken him from sleep.
He admitted to use of IV drugs including cocaine and heroin.
He had last injected himself with cocaine three days prior to
admission. He had injected with a clean, sharp needle. He had
no history of shooting into his leg veins or his abdomen. He
had had no trauma to his pelvis or hips. He had no cough, chest
pain, SOB, or sputum production. He had no history of TB, STD
or RHD or joint disease. He had no history of hepatitis and reported
a negative test for AIDS 18 months prior.
Three days prior to admission he was seen in the ER of another
hospital with similar complaints and a rectal temp of 103.8.
Labs had shown a WBC of 15,9000 and a II/VI systolic murmur was
noted. Admission was offered but the patient refused. He now
presented because of increased buttock pain which had progressed
to such a degree that he was unable to get out of bed.
Physical exam revealed an ill appearing young man. He was immobile
in bed and complained of severe pain. There was no swelling,
redness or fluctuance over the left SI area. He had full ROM
of the right hip which elicited pain in the left SI area. The
left hip also had full ROM and caused pain. Initial evaluation
included a CBC which showed a WBC of 17,200 (71P/3B/19L). He
was begun on broad spectrum antibiotics.
Imaging Findings
X-rays of the pelvis and hips showed destruction of the left SI
joint with loss of the joint space. There was sclerosis noted
on both sides of the joint. A Tc-99m MDP bone scintigram showed
increased activity on the flow image, the blood pool image and
the delay images in the region of the left SI joint. There was
also noted increased uptake in the left femur. A gallium-67 scintigram
was positive in the same regions with much increased uptake in
the left SI joint. Follow-up x-rays of the left femur showed
calcifications which appeared to be within the marrow and suspicious
of infarction. 5/5 blood cultures returned positive for a methacillin
sensitive Staph. Aureus. Antibiotic regimen was changed to nafcillin.
The patient improved rapidly.
Discussion
Anatomy:
The sacroiliac joint is composed of two opposing cartilaginous
surfaces -- a diarthroidal joint. It is bounded posteriorly and
above by strong interosseous sacroiliac ligaments. Anteriorly
is a thinner sacroiliac ligament which may be ruptured by trauma
or the pressure produced by a collection of material (pus) in
the joint cavity. Radiation of pain to the abdomen, hip, lateral
thigh and lower leg may be explained anatomically as the sacroiliac
joint opposes the retroperitoneum and four nerves pass close to
the joint capsule: the first two sacral nerves, superior gluteal
nerve and obturator nerve. These nerves can become irritated
due to inflammation in the area. Also, if the joint capsule ruptures,
the infected material can track through soft tissue anteriorly,
posteriorly, or inferiorly. Abscess formation may develop in
the gluteal region, the subgluteal region, the retroperitoneum,
along the iliopsoas either with or without peritonitis or through
the pelvic floor to the thigh, hip joint or the vaginal area.
Patient Characteristics and Presentation:
Conditions predisposing to pyogenic sacroilitis include trauma,
pregnancy, infections of the skin, osteomyelitis, urinary tract
infection, endocarditis, and drug addiction. The hormonal changes
of pregnancy induce laxity of the SI joint ligaments and allow
increased movement with the joint. Inflammation occurs which
enhances susceptibility to hematogenous seeding of bacteria.
Patients present in a variety of ways. The acute onset is characterized
by sudden onset of fever, pain, and decreased range of motion.
Subacute presentation may be with or without fever. There is
often malaise, pain, limp and some decreased range of motion,
but in general symptoms are vague. All patients have SI joint
pain, but this may be overlooked because of their reluctance to
move. SI joint pain may not be elicited during exam or may be
attributed to another source such as septic hip, psoas abscess,
malignancy, sciatica, herniated disc, pyelonephritis, ankylosing
spondylitis, or appendicitis. Subacute disease is difficult to
diagnose and the delay in proper diagnosis may lead to increased
morbidity, increased joint destruction, potential rupture and
abscess formation.
Work-up:
Appropriate clinical exam and laboratory evaluation are necessary
for accurate and early diagnosis. Physical exam is of the most
importance to localize pain and decreased motion. WBC and differential
may not be useful. Pragnatharthi found that 37%% of the patients
in his study of pyogenic sacroilitis had WBC less than 10,000.
Only 50%% demonstrated left shift. Positive blood cultures may
make the diagnosis, but many IV drug users will self medicate
themselves with "street antibiotics" (cephalexin) and blood cultures
may be negative. Synovial fluid cultures are technically difficult
to obtain because of the joint anatomy. Open biopsy and culture
may be required to establish diagnosis and identify the infectious
agent.
Literature:
There have been several studies on the utility of bone and gallium
scans in the diagnosis of osteomyelitis and sacroilitis.
Mauer:
This evaluation of the three-phase bone scan
commented on the benefit obtained from the flow and blood pool
images. Sensitivity was unchanged, but specificity was increased.
The false/positive rate was reduced.
Hogan:
This study of five cases of pyogenic sacroilitis
and review of the literature compared the blood pool image of
the bone scan with gallium images. He found the results to be
similar. For cost containment and convenience purposes he concluded
that gallium scan need not be performed regularly.
Bittini:
This study from 1985 took a somewhat different
approach. He compared acute presentation with late presenting
patients. He found gallium scans were positive when the bone
scans were negative in the acutely presenting patients. Both
scans were positive in the late presenting patients. He explained
the greater sensitivity of the gallium scan on the basis of the
different modes of deposition. Tc-99m MDP deposits because of
increased local blood flow and bone metabolic activity. Gallium-67-citrate
binds to proteins (albumin, haptoglobin, transferrin) and to PMN's
and macrophages. He concluded that gallium scans should be used
in the IV drug user population for any patient presenting with
vague complaints where an occult bone or joint infection may be
suspect.
Dye:
Studies performed with animal models have supported
Bittini's findings. New Zealand White Rabbits were inoculated
with S. Aureus and P. Aeruginosa and gallium and bone scans were
performed at various intervals. The results showed gallium more
sensitive earlier in the course of osteomyelitis. In the first
week 4/9 lesions were positive on gallium scan and only 1/9 had
a positive bone scan. In no instance was the bone scan positive
before the gallium scan.
Conclusions:
These studies and articles reviewed with this case discuss both
osteomyelitis and sacro-ilitis. Both infections are seen with
some frequency in the IV drug user population. Both bone and
gallium scans may be needed for accurate diagnosis of SI joint
infection. A negative bone scan may be seen early in the course
of osteomyelitis especially if there is no joint space infection.
A gallium scan should be done even with a negative bone scan
if clinical suspicion is high. In a patient who admits IV drug
use, who presents with vague complaints; aches and pains which
could be referable to bones or joints, a gallium scan may even
be done as the initial study before the bone scan.
References
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of Medicine. 1980; 69:50-56.
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3) Mauer A, et al. Utility of Three-Phase Skeletal Scintigraphy
in Suspect Osteomyelitis: Concise Communication. Journal Nucl.
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4) Horgan JG, Walker M, Newman J, Watt I. Scintigraphy in the
Diagnosis and Management of Septic Sacro-ilitis. Clinical Radiology.
1983; 34:337-346.
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6) Bittini A, et al. Comparison of Bone and Gallium-67 Imaging
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7) Waxman A, Bryan D, and Siemsen J. Bone Scanning in the Drug
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American Journal of Radiology. 1987; 149:1209-1211.
9) Prantharthi C and Narula A. Bone and Joint Infections in Intravenous
Drug Abusers. Reviews of Infectious Diseases. 1986; 8:904-911.
10) Graham GD, Lundy MM, Frederick RJ, et al. Scintigraphic Detection
of Osteomyelitis with Tc-9m MDP and 67 Gallium Citrate: Concise
Communication. Journal Nucl Med 1983; 24:1019-1022.
11) Jajic I, Furst Z, et al. Septic Sacroilitis. Acta Orthop
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12) Shapiro S and See C. Pyogenic Sacroilitis Minnesota Medicine.
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J. Anthony Parker, MD PhD, Tony_Parker@bidmc.harvard.edu