CASE 1962 Published on 18.01.2003

Unusual hip problem in a patient with ankylosing spondylitis

Section

Musculoskeletal system

Case Type

Clinical Cases

Authors

B. Sankar, G. Kumar, K. Iyengar, B.N. Livingstone

Patient

57 years, male

Clinical History

The patient, who was known to be suffering from ankylosing spondylitis, presented with a two-day history of pain in the region of the left hip. He was looking well with a temperature of 37.2°C. Blood tests revealed a raised WBC count and CRP. Two days later he became drowsy and disoriented with tachycardia of 140 beats/minute. An electrocardiogram revealed fast atrial fibrillation and his biochemical blood parameters were indicative of renal shutdown.

Imaging Findings

The patient presented with a two-day history of spontaneous, localised, throbbing pain in the region of the left hip that was severe enough to prevent him from weight bearing on the left leg. He was already known to be suffering from ankylosing spondylitis, involving both hips, for which he was on oral anti-inflammatory medications.

On presentation he did not have fever, rigors, malaise or loss of appetite. The movements at the left hip were grossly reduced, but available ranges of movement were painless. He was looking well with a temperature of 37.2°C. Blood tests revealed a white cell count of 19.2 x 109/L with neutrophils of 17.7 x 109/L, a C-reactive protein (CRP) level of 151mg/L and erythrocyte sedimentation rate of 7mm in the first hour. Blood cultures were performed as the WBC count and CRP were raised.

Anteroposterior radiographs of the pelvis - both hips (Fig. 1) and the left hip only (Fig. 2) - revealed protrusio acetabuli. He was admitted for pain relief with a provisional diagnosis of an acute flare up of ankylosing spondylitis.

Two days later the patient became drowsy and disoriented with tachycardia of 140 beats/minute. Opiate narcosis was suspected and he responded at least initially for a short while to intravenous naloxone. An electrocardiogram revealed fast atrial fibrillation and his biochemical blood parameters were indicative of renal shutdown. The patient was transferred to the intensive therapy unit for cardioversion and haemofiltration.

Forty-eight hours after presentation the initial blood culture reports came back as positive for Staphylococcus aureus. Ultrasound examination of the left hip showed the presence of fluid in it. Arthrotomy of the left hip revealed frank pus in the joint, from which Staphylococcus aureus was later isolated. The joint was thoroughly lavaged. The patient was treated with intravenous vancomycin and remained in the intensive therapy unit until his cardiac and renal functions returned to satisfactory levels. He showed good improvement with respect to symptoms and the surgical wound healed without complications.

Discussion

Increased pain in peripheral joints affected by any chronic inflammatory arthritic process, is usually attributed to flare up and progression of the disease and managed with appropriate alterations in the use of analgesics. Clinical differentiation between flare up of arthritic process and joint infection can be extremely difficult. Haematological parameters are often non-specific and plain radiographic changes are difficult to assess when sepsis occurs in an already damaged joint. Due to these reasons, the diagnosis of infection is often delayed and is possible only at a stage when joint destruction is advanced. This explains the high morbidity and mortality reported (1).

In the case presented here, the dramatic sequence of events that occurred when the patient became septicaemic led to an early diagnosis and appropriate management.

Recognised risk factors for adult septic arthritis include immunocompromised state, inflammatory diseases like rheumatoid arthritis (2), destructive joint diseases like osteoarthritis, gout etc. and joint prostheses (3). In fact any form of arthritis, by means of damaging the joint surfaces, can theoretically predispose it to sepsis. However, for unknown reasons, infection in joints with pre-existing ankylosing spondylitis is extremely rare with only two case reports so far (4,5).

The portal of entry of pathogenic bacteria in ankylosing spondylitis has been postulated previously to be through an abnormal gastrointestinal tract (4), but this is very unlikely in this case since the infective organism was Staphylococcus aureus. In the case presented, in spite of detailed examination and investigations, no source of bacteraemia could be identified.

We conclude that the possibility of infection should be borne in mind even when the underlying disease is a sero-negative arthropathy. It can occur without an identifiable source of bacteraemia elsewhere in the body. As in children, a high degree of suspicion is necessary for early diagnosis and management of sepsis in an adult joint with pre-existing arthritis, to avoid potentially serious and fatal complications. One should have a very low threshold for aspirating the joint even when the diagnosis is a flare up of arthritis. Ultrasound-guided aspiration is of great value in joints difficult to aspirate, like the hip. Leukocyte scans, though equally informative, are expensive and not readily accessible to everyone.

Differential Diagnosis List
Staphylococcal septicaemia from septic arthritis in ankylosing spondylitis
Final Diagnosis
Staphylococcal septicaemia from septic arthritis in ankylosing spondylitis
Case information
URL: https://eurorad.org/case/1962
DOI: 10.1594/EURORAD/CASE.1962
ISSN: 1563-4086