bubble_chart Overview

Actinomycosis of bone is a rare deep fungal infection, occasionally seen in the northwestern regions of China, predominantly affecting rural populations. The disease most commonly occurs in individuals aged 11 to 30 years and is characterized by the formation of multiple sinus granulomas. A distinctive feature is the discharge of purulent fluid containing "sulfur-colored granules" from the sinuses. Cattle and horses can also contract this disease.

bubble_chart Pathogen

Actinomycetes are filamentous fungi, often arranged in a radial pattern, found in soil with a wide variety of species. The pathogenic type is *Actinomyces bovis*. This bacterium is Gram-positive and exhibits anaerobic characteristics. In healthy individuals, actinomycete hyphae can be found in dental caries and tonsillar crypts, morphologically identical to pathogenic strains. Apart from *A. bovis*, five other types have been identified. Pathogenic strains typically grow and spread under conditions of tissue hypoxia and reduced resistance (often after tooth extraction or inflammation), entering the mandibular angle and neck from the oral mucosa. They may also invade the lungs via the respiratory tract, causing pulmonary lesions, or the ileocecal region via the digestive tract. Actinomycetes primarily spread directly through connective tissue to surrounding areas, rarely via the bloodstream, and never through the lymphatic system—a defining characteristic. Lesions may extend to involve bones, with most bone lesions being secondary.

bubble_chart Pathological Changes

The pathological manifestations primarily consist of chronic suppurative granulomatous inflammatory masses. The primary lesions are mostly located in the subcutaneous tissue and submucosa, with multinucleated cells and mononuclear cells infiltrating around the actinomyces. The outer layer contains fibroblasts and foreign body giant cells, along with abundant reticular capillaries. The granulation tissue softens to form scattered small abscesses, which subsequently rupture to form multiple fistulas. The discharge is purulent with yellow "sulfur granules," eventually leading to scar formation. Both acute and chronic inflammation coexist in the lesions. The bacteria have a lytic effect on various tissues, so the disease spreads by directly invading surrounding tissues. Common sites of infection are the cervicofacial region, accounting for over 50%, followed by the chest and abdomen.

Bone lesions initially start from the periosteum, then invade the cortical bone, and finally enter the medullary cavity, often secondary to direct spread from soft tissues. Bone lesions manifest as inflammatory sexually transmitted disease changes with alternating destruction and proliferation. In mandibular lesions, significant bone destruction is often observed without new bone formation, and sequestra are generally absent. In the spine, new bone formation is more common, so kyphotic deformities due to vertebral collapse are rare. The intervertebral discs usually remain intact. However, the disease often involves the vertebral appendages and rib heads.

bubble_chart Clinical Manifestations

The patient may exhibit systemic infectious symptoms such as fever, malaise, anemia, etc. However, the primary manifestations are local inflammatory signs. When the mandible is involved, it often begins with toothache, followed by swelling of the alveolar ridge, loose teeth, accompanied by grade I pain, swelling of the buccal soft tissues, and thickening of the mandible. Inflammatory granulomatous masses may soften and rupture, discharging pus containing yellow "sulfur granules" composed of bacterial colonies, forming multiple fistulas that heal into irregular, tough scars. Lesions in the maxilla may extend intracranially to the cerebral membrane and brain. Lesions below the jaw may spread to the neck and chest, while posterior extension can reach the cervical vertebrae. Thoracic lesions may invade the ribs and thoracic vertebrae, and ileocecal lesions may involve the pelvis and lumbar vertebrae.

If vertebral bodies are affected, the lesions may spread upward and downward along the anterior longitudinal ligament, involving multiple vertebrae. The destructive process may extend posterolaterally to the vertebral arches, transverse processes, necks and heads of the ribs, and eventually the spinous processes, all of which may be destroyed. However, the intervertebral discs often remain intact. At this stage, the patient's clinical symptoms and signs are not severe, with only grade I pain and tenderness, and grade I limitation of spinal movement.

bubble_chart Auxiliary Examination

The radiographic findings mainly show irregular, poorly marginated osteolytic destruction and osseous sclerosis. The mandible may become enlarged and thickened, possibly accompanied by fistula formation. When vertebrae are involved, a honeycomb-like radiolucent appearance can be observed, resulting from osteoporotic destruction areas surrounded by osteosclerosis and hyperostosis, with rare vertebral collapse.

Laboratory tests: The primary examination involves fungal detection, where sulfur granules in pus can reveal Actinomyces. Crushing sulfur granules between two glass slides and examining under a microscope shows radiating mycelium. Anaerobic culture media can also be used for Actinomyces cultivation.

bubble_chart Diagnosis

The diagnosis of this disease is not difficult, as the lesions in the mandible of the face and neck are quite distinctive. Clinically, the presence of chronic suppurative granulomatous masses that subsequently ulcerate, discharge pus containing yellow "sulfur granules," and form multiple fistulas aids in diagnosis. The clinical manifestations of vertebral involvement and the characteristic X-ray changes in the vertebral body and its appendages also exhibit specific features. Of course, in differential diagnosis, it is important to distinguish it from chronic bone inflammation and subcutaneous nodules of the bone. Chronic inflammation often has a history of acute inflammation, ulceration with pus discharge, and sequestrum formation, but the pus lacks yellow granules. Vertebral subcutaneous nodules involve destruction of multiple intervertebral discs, with fewer affected vertebral bodies, and the transverse processes and rib heads are usually not damaged. Cold abscesses do not contain yellow granules, and the spine often presents with kyphotic deformity. Naturally, the most convincing confirmation of this disease is the identification of radially arranged fungal filaments within the sulfur granules.

bubble_chart Treatment Measures

It is relatively difficult. Since a definitive diagnosis cannot always be made in the early stages (such as lesions in the chest, abdomen, or spine), early treatment is often unavailable, and the prognosis is generally poor.

Surgical intervention is commonly employed, involving incision and drainage as well as the excision of necrotic tissue. The affected area should be exposed to air as much as possible. High doses of antibiotics, with penicillin as the first choice, are administered before and after surgery. A daily dose of 2 to 6 million units is maintained for several months. Sulfadiazine and iodides may sometimes be used in combination. Supportive therapy is provided for patients in poor general condition. Radiation therapy may also be applied to lesions in the facial and cervical regions.

Maintaining oral hygiene and preventing infection are crucial. For instance, timely use of antibiotics after tooth extraction can also play a positive role in preventing the occurrence of actinomycosis.