Mucor spores are ubiquitous in the natural environment. If healthy people inhale spores, macrophages and neutrophils phagocytose the oxidized spores to prevent fungal invasion. However, these cells cannot inhibit spore germination and kill hyphae effectively in immunocompromised patients (those with neutropenia, diabetic ketoacidosis, immunosuppressive therapy and so on). Disorders of these cells are key factors in vascular invasion . Our patient suffered from diabetes, ketoacidosis and pulmonary mucormycosis, in line with the literature. Nevertheless, mucormycosis is seldom seen in vertebral or paravertebral soft tissue. To the best of our knowledge, osteomyelitis caused by mucor infection is uncommon but has been described in the tibia, femur, humerus, scapula, metacarpal, phalanx, sternum, cuboid, calcaneus, tibia, internal fixation and repaired anterior cruciate ligament . Mucormycosis spondylitis is very rare in clinical practice. To date, only 10 literatures of mucormycosis osteomyelitis have been reported in the English-language literature, according to a search of PubMed, Embase. The data of all these cases are summarized in Table 1. The average age of patients with spinal mucormycosis involvement is 50.2 years. Males account for 63.6%, and the mortality rate of patients with spinal involvement is 63.6%, slightly higher than the 54% reported in the literature for mucormycosis without spinal involvement . Four patients have suffered from diabetes (2 with ketoacidosis), 2 malignant tumors, 1 MDS (myelodysplastic syndrome), 2 renal insufficiency, 1 hypohepatia, and only 1 without underlying disease. In our case, thoracic spine involvement, vertebral osteomyelitis, spinal cord compression and paraspinal soft tissue abscess were evidenced. Approximately 2 months after the symptoms the disease was diagnosed as mucormycosis (35 days in first hospital and 23 days in second) which also showed that delay in diagnosis and initiation of appropriate therapy with antifungals was the major reason for dissemination of the disease. Delays to diagnosis and treatment can be a possible cause of disease transmission and death. In conclusion, the thoracic vertebrae are the most easily affected sites in mucormycosis spondylitis, while cervical or sacral involvement is unusual. Special attention should be given when the suspected diagnosis is mucormycosis spondylitis and timely antifungals treatment should be given.
Most mucormycosis spondylitis cases are not treated with surgery. Buruma et al.  reported the first mucormycosis spondylitis patient, who had a history of laryngectomy and radiotherapy and became paralyzed as a result of cervical mucormycosis. The patient died of pulmonary embolism and cervical spondylitis of mucormycosis, which was confirmed by autopsy and pathological examination. Hadgaonkar et al.  reported isolated mucormycosis spondylitis in a patient with a history of diabetes, hypertension, chronic nephropathy and dialysis. The patient's MRI showed that only the L4–L5 vertebrae had an abnormal signal intensity, and no other lesions existed. Mucor infection was confirmed by lumbar biopsy. The patient died of septicemia and multiple-organ failure. Machida et al  reported a patient with myelodysplastic syndrome associated with subacute myelopathy who received local radiotherapy, which was ineffective. Autopsy confirmed that fungal exudates blocked the anterior vertebral artery and resulted in spinal cord infarction. Giuliani et al.  reported a case of an infection in the thigh and hip skin that disseminated to the T10–T12 vertebrae. CT showed no bony destruction, but MRI showed osteomyelitis. Paraplegia was caused by spinal cord infarction due to obstruction of the arteriae spinalis anterior. After debridement of the skin and subcutaneous infection, the patient was discharged from the hospital after 3 months, without any recovery of the paraplegic symptoms.
Only 3 patients received surgical debridement of infected vertebral and paravertebral soft tissue. Chen et al.  reported a case of lumbar vertebrae mucormycosis after disc puncture. The patient underwent repeated posterior debridement. The patient eventually recovered with oral medication for another 8 weeks. Both Navanukroh et al.  and Rozich et al.  reported similar cases of disseminated primary lung mucormycosis that spread into the lumbar vertebrae. Both patients underwent posterior necrotic tissue debridement, laminectomy and decompression of the spinal canal. One patient died, and the other patient survived. The case we present is the first case in which thoracic vertebrae were involved in mucormycosis. He underwent posterior spinal surgery. The patient developed severe pulmonary infection and rapid progression of paraplegic symptoms, so we performed debridement and decompression. After timely operation and intravenous injection of amphotericin B, which was effective against the Mucor, the patient was generally in good condition, and his paraplegia symptoms partly recovered. The reason for the incomplete recovery might be that Mucor invades and blocks blood vessels, which results in ischemic and irreversible damage to the spinal cord. If such a case does not permit surgery as early as possible, irreparable sequelae will result . Regrettably, the patient died of bleeding of the urinary system due to aggravation of residuary lung lesions.
Mucormycosis spondylitis and paraspinal abscess have different clinical manifestations. As described in Table, the general symptoms of mucormycosis spondylitis include malaise, weight loss, fever, local symptoms of pain (most common), nerve damage (radiculopathy, myelopathy and cauda equina syndrome), paralysis, etc. . It is difficult to distinguish mucormycosis spondylitis from other spondylitis through imaging. Mucormycosis spondylitis cannot be diagnosed directly by clinical manifestations, laboratory examination and imaging. The positive rate of tissue culture is not high, so a definite diagnosis requires biopsy and confirmation of the special morphology of the hyphae . In this case, the appearance of paraplegic symptoms was caused by direct invasion of the primary pulmonary mucormycosis. Etiological tests were negative, empirical use of antibiotics was inefficient, and the specific type of spinal infection could not be clarified by imaging. The correct diagnosis depends on the observation of specific hyphae in debridement tissue on pathological examination.
Therapeutic measures to treat mucormycosis include early diagnosis, systemic antifungal therapy, basic disease control and aggressive surgical debridement . To date, the survival rates have increased since amphotericin B has been introduced to treat mucormycosis, but they are still low. In the study of Roden et al. , surgical debridement was an independent risk factor for survival rates in patients with mucormycosis. Mucor shows vascular invasiveness and blocks the vascular lumen with mycelium and exudates, which makes antifungal drugs ineffective [3, 18]. Therefore, surgical debridement is more important for curing the disease. For patients with spinal cord compression, surgical debridement not only saves patients' lives but also benefits their functional recovery and the improvement of their quality of life as soon as possible.
Internal fixation has a positive effect on maintaining spinal stability and facilitating the clearing of infections in spinal infectious diseases . To our knowledge, this is the first patient who underwent unilateral laminectomy, decompression of the spine and pedicle screw implantation. An internal fixation device was applied for mucormycosis spondylitis, and the patient recovered well. Unfortunately, due to the sudden death of the patient, long-term follow-up on this surgical method was impossible. There is no consensus about whether to use an internal fixation device and what kind of operation should be carried out for this disease among experts in various countries, so it is necessary to study more cases and large samples of randomized patients.
Spinal or paraspinal tissue-involved mucormycosis is seldom seen in the clinic and has a high mortality rate. Doctors must remain alert and aware of scarce spinal infectious diseases and do comprehensive clinical evaluations and pathological biopsies to diagnose them early. Multidisciplinary team diagnosis and treatment is particularly valuable for such diseases. It mainly involves surgery, internal medicine to adjust blood glucose, infection department to anti-infection treatment. Orthopedic surgeons should design appropriate and individualized surgery plans for spine-involved mucormycosis patients.