A 67-year-old Caucasian woman was seen at our clinic for possible prosthetic infection following a total left hip replacement. Her medical history was negative until three years before, when she began to complain of left hip pain during walking, movement limitation, and pain at rest. After one year of unsuccessful prior rehabilitative and analgesic treatment, she underwent total left hip replacement. The results of a pre-operative chest X-ray and blood tests were normal; however, erythrocyte sedimentation rate (ESR) was elevated (94 mm/hour). The post-operative period was uneventful, and the patient was discharged five days after surgery. She remained in good clinical condition until about 16 months after surgery, when she began to feel pain and movement limitation at the prosthetic site. Two months later, a hip computed tomography (CT) scan showed a suspect iliopsoas abscess, which was confirmed by peripheral blood mononuclear cells marked with 99 mTc. Her clinical conditions worsened because of increasing local pain and an irregular mild fever. She was admitted to an orthopedic unit for needle aspiration of the abscess (102 x 53 mm) under ultrasound guidance. Culture of the needle aspiration and blood cultures for aerobic and anaerobic bacteria were performed, and empiric antibiotic therapy was started with intravenous linezolid (600 mg twice a day). Her fever increased, and all cultures were negative. After one week of unsuccessful medical treatment, the surgeon decided to perform surgery to inspect and clean the infected site.
A pseudocyst containing dense material was found just near the prosthesis. A complete aspiration with culture of dense and cloudy liquid, including biopsies of the wall of the cyst and the surrounding tissue, was performed. Intravenous antibiotic therapy with 400 mg of teicoplanin, 160 mg of gentamicin, and 800 mg of ciprofloxacin was started. After four days, the fever disappeared and the patient was discharged without antibiotic therapy. Repeat cultures were negative. A histopathological examination disclosed a fibrous tissue with acute and chronic inflammation, partly with an aspecific granulomatous aspect.
Twenty days later, the patient complained of mild fever and a painful, fluctuant nodule located at the superior internal surface of the left thigh along the surgical scar. The nodule was then surgically drained. A large quantity of cloudy liquid was collected from the site. Cultures were again negative. At the site of the cut, there appeared to be a deep fistula of about 5 cm in diameter with discrete, greenish, and odorless secretion. There was no evidence of inflammation to the surrounding tissues. The patient was then admitted to our unit. Her vital signs were normal. During a physical examination, she showed bad general health conditions and evident brownish coloration of the skin to the extremities (hands, feet, palmar, and plantar plicae), nipples, linea alba, and oral mucosa. The cutaneous fistula appeared unchanged. Laboratory studies showed the following: red blood cell count of 4.53 x 109/L, hemoglobin of 12.9 g/dL, platelet count of 336 x 109/L, white blood cell count of 8.2 x 109/L (60.9% neutrophilis and 24.2% lymphocytes), ESR of 89 mm/hour, and C-reactive protein (CRP) of 75 mg/L (normal value is less than 0.5 mg/L). The result of a tuberculin skin test (5 IU purified protein derivative) was positive, QuantiFERON-TB Gold was 3.08 IU/mL (cutoff value is 0.35 IU/mL), serum cortisol at 8 a.m. was 9.5 mug/dL (normal value is 4.3 to 22.4), adrenocorticotropic hormone (ACTH) was 2300 pg/mL (normal value is 10 to 60), and anti-cortex antibodies were negative. The second controls of serum cortisol and ACTH were 5.5 mug/dL and 1490 pg/mL, respectively. Major causes of adrenal insufficiency are autoimmune disorders and MTB infection. Anamnesis, CT scan of adrenal glands, and the absence of anti-cortex antibodies suggested exclusion diagnosis of Addison disease secondary to MTB infection. The result of an experimental whole blood test based on interferon-gamma (IFNgamma) response to RD1-selected peptides, which tends to be related to active tuberculosis, was also positive. The active IFNgamma response was 2.6 IU/mL (cutoff is 0.7 IU/mL). The remaining biochemical parameters were normal. The amount of secretion was discrete; thus, fistula microbiological cultures could not be done. A single specimen was collected to perform Gram and Ziehl-Neelsen staining. Only polymerase chain reaction (PCR) for MTB complex was positive.
Hip, abdominal, and chest CT scans revealed a periprosthetic abscess with diffusion to the left psoas muscle (Figure 1), a slight bilateral adrenal enlargement with calcifications, and a mild fibrosis of both upper lobes of the lungs. Our patient's condition was diagnosed on the basis of the laboratory and clinical findings as tuberculosis and secondary Addison disease. So that Pott disease could be excluded, our patient underwent a backbone X-ray, which was negative. She was put on treatment with anti-tuberculosis agents: rifampicin (RFP), ethambutol, isoniazid (INH), pyrazinamide, and pyridoxine without removal of the prosthesis. Hydrocortisone and fludrocortisone were prescribed for Addison disease. After three months, the anti-tuberculosis treatment was continued with RFP and INH only. The fistula continued to slowly discharge discrete amounts of secretion and appeared to be completely healed after six months. Our patient was totally asymptomatic and without pain upon hip movements after 15 months. The iliopsoas abscess was no longer evident on a CT scan performed about one year later.