Septic Sacro-Ilitis in an IV Drug User
Gail P. Sorrel, M.D.
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.
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.
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.
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.
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.
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.
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J. Anthony Parker, MD PhD, firstname.lastname@example.org