A 5-year-old girl was admitted to our hospital due to a history of recurrent pain, erythema, swelling, festering sores on the right lower extremity, and discharged pus from a sinus in the right foot for 8 months. The routine antenatal ultrasound examination showed congenital absence of the right kidney, without a remarkable family history. The girl was born at full term with a low birth weight of 2000 g. She had nonsyndromic polydactyly in the right foot. A pustule on her right foot was observed after 3 days of birth, and her mother pricked it with a needle. A sinus was left after pus discharged from the wound for several days. At the age of 2 years, surgery was performed to remove the extra toes from the right foot at a local hospital.
The patient’s symptoms occurred 8 months prior to her admission to our hospital. She initially presented with pain, erythema, and swelling in the right popliteal fossa, accompanied by a high fever of 39 °C. Incision and drainage were performed at a local hospital, and then the symptoms improved. However, the patient’s symptoms reoccurred after 1 week of discharge, and drainage and intravenous cephalosporin were applied. Since then, the patient suffered recurrent episodes of pain, erythema, and swelling in her right popliteal fossa, which gradually extended to the right lower limb at 3 months prior to admission.
On admission, physical examination revealed that the patient’s liver and spleen were not palpable. The cardiovascular system, respiratory system and central nervous system showed no abnormalities. A scar of approximately 10 cm and a swollen area were found on the right popliteal fossa (Fig.
1A). Two sinuses on the right crus (Fig.
1B) and a draining sinus on the lateral side of the foot (Fig.
1C) were noted. Laboratory tests showed an elevated white blood cell count (WBC, 18.47 × 10
9/L, reference range: 8–12 × 10
9/L), C-reactive protein level (CRP, 108 mg/L, reference range: <5 mg/L), procalcitonin level (PCT, 0.15 ng/ml, reference range: <0.1 ng/mL), and erythrocyte sedimentation rate (ESR, 22 mm/h, reference range: 0–20 mm/h). The T-SPOT tuberculosis (TB) test, blood culture, bone marrow culture and smear were negative. Ova and parasite tests and parasite antigens were negative. Analyses of coagulation function and liver biochemical profiles were normal. Tumor markers (alpha-fetoprotein, carcinoembryonic antigen) and autoantibodies were negative. Lymphocyte subset analysis and immunoglobulin and neutrophil NADPH oxidase activity were normal. X-rays were unremarkable. Magnetic resonance imaging (MRI) revealed abnormal signal shadows in the inferior cortex, subcutaneous tissues of the popliteal fossa and behind the right crus (Fig.
2A, blue arrow) and tibiofibular bone marrow edema (Fig.
2B, green arrow), suggesting soft tissue infection and osteomyelitis. Bacterial culture of the pus extracted from the festering sore on the right popliteal fossa (blood AGAR, 37 °C, 72 h) detected the growth of
Actinomycetes europaeus, which was confirmed by colony morphology, bacterial Gram stain smears (Fig.
3, ZEISS Primostar), and mass spectrometry. Therefore, the patient was diagnosed with musculoskeletal actinomycosis and was given intravenous ampicillin-sulbactam therapy. After 4 weeks of intravenous ampicillin-sulbactam (55 mg/kg, q8 hr) treatment, the patient’s symptoms persisted. Then, MRI was performed again, which showed that the bone marrow edema of the right tibiofibula had been resorbed (Fig.
2D, yellow arrow). However, the sagittal view of right lower extremity MRI scan showed the infection of the soft tissue had progressed, possibly involving the right gastrocnemius muscle with pus cavity formation (Fig.
2C, orange arrow). Considering the extensive lesions of the right crus and the presence of sinus tract in the patient, debridement was performed at the Department of Orthopedics. Large amounts of chronic inflammatory granulation tissue, disorganized fibrous connective tissue, and a sinus tract were observed (Fig.
4A). Irrigation was performed after removing the inflammatory granulation, fibrous connective tissue, and sinus tract, and a negative pressure drainage ball was placed. Pathological examination of a biopsy specimen from the sinus tract showed local fibrous hyperplasia with collagenization, endovillage squamous epithelium with hyperkeratosis, surrounding inflammatory cell infiltration, sinus tract formation (Fig.
4B, LEICA DM500), granulomatous inflammation with lymphoid hyperplasia, and hyperplasia with multinuclear giant cell reaction (Fig.
4C, LEICA DM500). The patient was discharged with significant symptom improvement after an additional 3 weeks of intravenous ampicillin-sulbactam (55 mg/kg, q8 h) treatment. Another 6 weeks of maintenance therapy with oral amoxicillin (32 mg/kg, q8 h) and clavulanate (9.2 mg/kg, q12 h) was given to the patient after discharge, and a favorable outcome was achieved.
The first follow-up was performed at the Department of Orthopedics after 2 weeks of discharge. The patient’s wound surface had healed, no articular contracture was found, and the MRI scan was unremarkable. The second follow-up was performed at the Department of Gastroenterology, Hepatology and Nutrition after 1 month of discharge. There were no fever, swelling, pain, or pus, and the routine blood tests were normal, including WBC count, ESR, and CRP levels. Then, the patient was followed up every month by phone. To date, there were no symptoms of recurrence, such as pain, erythema, or swelling, during the 15-month period of follow-up. Currently, monthly follow-up is ongoing to monitor the possible disease recurrence of the patient.