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Infectious Diseases and Microbiology: Low Back Pain and Fever
Basics
Description
Back pain refers to acute or chronic pain arising from the spine or paraspinal structures. The combination of back pain and fever requires careful evaluation for nonmechanical causes. History should specifically assess weight loss, pain worse when lying down, morning stiffness, and sudden severe or colicky pain. Serial spinal and neurologic examinations are crucial, and any spinal tenderness or focal pain warrants full diagnostic assessment. Vertebral osteomyelitis is commonly suggested by pain worsened by movement and not relieved by rest, focal vertebral tenderness, and elevated erythrocyte sedimentation rate. Pain from neoplastic nerve infiltration is typically constant, progressively worse, and persists at night without relief, whereas mechanical low back pain usually improves with rest. Work-up often begins with plain radiography followed by bone scintigraphy, MRI, CT, laboratory testing, and biopsy based on abnormal findings.
Epidemiology
A definitive pain source is difficult to establish and is identified in fewer than one-quarter of cases. Mechanical causes account for about 97% of low back pain, with degenerative disk disease and lumbar sprain/strain comprising most cases. The spine is a frequent site of bone metastasis. Vertebral osteomyelitis is uncommon at roughly 1 per 100,000 persons annually, with rising rates attributed to vascular devices and intravenous drug use; it occurs more often in early childhood and in adults over 50. Spinal epidural abscess occurs in about 1 per 10,000 hospital admissions per year, and MRSA-related vertebral osteomyelitis and epidural abscess are increasingly reported. Despite global increases in tuberculosis, the rate of extrapulmonary spinal disease remains relatively stable; Pott disease, typically involving the lower thoracic vertebrae, is the most common musculoskeletal extrapulmonary manifestation. Improved survival in sickle cell disease has been accompanied by more Salmonella vertebral osteomyelitis.
Risk Factors
Infectious complications can follow bites from many animals, often linked to occupational exposure (farmers, laboratory workers, veterinarians) or recreation (hunters, campers, exotic pet owners). Systemic infection after animal or human bites is more likely with extremity edema or impaired lymphatic drainage and in immunocompromised hosts. Fever after a dog bite in an immunosuppressed patient should prompt concern for invasive Capnocytophaga canimorsus infection.
Etiology
Infectious sources of back pain with fever include biliary tract infection, chronic prostatitis, herpes zoster, pyelonephritis, retroperitoneal abscess, spinal epidural abscess, and vertebral osteomyelitis. Noninfectious causes include colonic cancer, pancreatic disease, histiocytosis X, metastatic malignancy (breast, lung, prostate, thyroid, kidney, gastrointestinal tract), multiple myeloma, neoplastic invasion of pelvic nerves, lymphoma, pregnancy, vertebral fracture, renal artery or vein thrombosis, renal stones, retroperitoneal hemorrhage or tumors, and tumors of the posterior stomach or duodenum. Staphylococcus aureus is the leading cause of spinal epidural abscess, accounting for most reported cases, with additional pathogens including Actinomyces israelii, Aspergillus, Blastomyces, Brucella, Cryptococcus, Haemophilus parainfluenzae, Mycobacterium tuberculosis, and Streptococcus milleri. Vertebral osteomyelitis is most often due to staphylococci but may be caused by other bacteria or tuberculosis; one multicenter retrospective study from southern Spain reported a high proportion due to Brucella, with the remainder split between pyogenic and tuberculous disease.
Commonly Associated Conditions
Vertebral osteomyelitis and spinal epidural abscess are frequently associated with diabetes, injection drug use, chronic renal failure, alcohol use disorder, bacteremia or focal infections, and malignancy. Most epidural abscesses arise via hematogenous spread from skin or mucosal sources, though direct extension from adjacent infection is also recognized. Postoperative abscesses account for a substantial minority, and epidural catheter placement is another risk factor. Blunt trauma may precede symptoms and may lead to an epidural hematoma that later becomes infected.
Diagnosis
Spinal epidural abscess classically presents with fever, spinal pain and tenderness, and radicular pain progressing to limb weakness, with pain being the most consistent feature. Early on, spinal pain with or without fever may be the only findings before sudden neurologic decline. When sepsis dominates or when patients are bedbound, neurologic deficits may be missed. Fever is absent in a notable minority of pyogenic vertebral osteomyelitis cases and is even more commonly absent in tuberculous vertebral osteomyelitis.
History
Key elements include age; systemic symptoms such as fever, weakness, weight loss, and night sweats; prior trauma, infection, or cancer; pain characteristics; immune status; glycemic control in diabetes; and injection drug use. Screen for neurologic complaints including weakness, paresthesias, numbness, and bowel, bladder, or sexual dysfunction. Risk is higher in patients over 50, those using steroids, individuals with HIV, those on immunosuppressants, and those with prior surgery.
Physical Examination
Assess general appearance, vital signs, peripheral pulses, and perform a focused cardiopulmonary and abdominal evaluation in unstable patients. Look for referred pain by examining potential primary sources of tenderness. Perform a complete neurologic examination to evaluate for spinal cord compromise and localize deficits; lesions below T12 can produce lower motor neuron findings, and cauda equina syndrome may include bowel or bladder incontinence. In older adults, fever may be low-grade and does not reliably indicate severity. Percussion of spinous processes may reveal focal vertebral tenderness due to trauma, malignancy, or infection. Examine for signs of endocarditis and septic emboli.
Diagnostic Tests and Interpretation
Laboratory Studies
Routine blood tests are often nonspecific for vertebral osteomyelitis, but leukocytosis, neutrophilia, and markedly elevated ESR and C-reactive protein support pyogenic disease. Blood cultures are the most useful routine test and identify the organism in about half of pyogenic and Brucella vertebral osteomyelitis cases. Bone biopsy is often required to confirm the diagnosis, especially in tuberculous disease.
Imaging
Plain spinal radiographs may be normal early in vertebral osteomyelitis. MRI best defines the extent and location of spinal epidural abscess. MRI or CT myelography is preferred when spinal metastasis is suspected.
Diagnostic Procedures/Other
CT-guided needle biopsy reliably diagnoses carcinoma but is less dependable for lymphoma, though performance has improved with CT guidance, immunophenotyping, and larger needles; false-negative rates remain significant. Establishing an etiologic diagnosis of vertebral osteomyelitis often requires percutaneous or surgical vertebral biopsy.
Differential Diagnosis
Tuberculosis may appear early as an opportunistic infection in AIDS and can be AIDS-defining, while Mycobacterium avium complex typically occurs later with very low CD4 counts. Pertussis should be considered when cough is the predominant symptom, particularly with paroxysms, inspiratory whoop, posttussive vomiting, sleep-disrupting cough, or exposure to similar illness.
Treatment
Medications
Suspected vertebral osteomyelitis or epidural abscess warrants empiric vancomycin to cover MRSA, with addition of a third- or fourth-generation cephalosporin when gram-negative bacteremia is suspected, especially with concurrent pyelonephritis. Therapy should be narrowed once the pathogen is identified; for methicillin-sensitive S. aureus, options include nafcillin, oxacillin, or cefazolin. Typical duration is at least six weeks. Management of tuberculous, brucellar, and salmonella bone disease follows their respective regimens. Corticosteroids may help in acute spinal cord compression. NSAIDs provide symptomatic analgesia, and bisphosphonates may be used for fractures related to breast cancer metastases.
Additional Treatment
Prompt diagnosis with targeted therapy is essential. Epidural abscess requires urgent surgical management with early decompression plus antibiotics. Spinal cord compression is a neurosurgical emergency, and decompression via surgery or radiotherapy within 24 hours of symptom onset is needed to reduce permanent neurologic injury. In suspected spinal or paraspinal infection, bactericidal empiric antibiotics should be started immediately.
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Ongoing Care and Follow-Up
If symptoms persist beyond six weeks, repeat laboratory testing and imaging are recommended. After six weeks of antibiotics for osteomyelitis or epidural abscess, reassessment is needed to determine whether treatment should continue. Ongoing monitoring for medication toxicity is important, particularly in older adults who are more susceptible to adverse drug effects.
Basics
Description
Back pain refers to acute or chronic pain arising from the spine or paraspinal structures. The combination of back pain and fever requires careful evaluation for nonmechanical causes. History should specifically assess weight loss, pain worse when lying down, morning stiffness, and sudden severe or colicky pain. Serial spinal and neurologic examinations are crucial, and any spinal tenderness or focal pain warrants full diagnostic assessment. Vertebral osteomyelitis is commonly suggested by pain worsened by movement and not relieved by rest, focal vertebral tenderness, and elevated erythrocyte sedimentation rate. Pain from neoplastic nerve infiltration is typically constant, progressively worse, and persists at night without relief, whereas mechanical low back pain usually improves with rest. Work-up often begins with plain radiography followed by bone scintigraphy, MRI, CT, laboratory testing, and biopsy based on abnormal findings.
Epidemiology
A definitive pain source is difficult to establish and is identified in fewer than one-quarter of cases. Mechanical causes account for about 97% of low back pain, with degenerative disk disease and lumbar sprain/strain comprising most cases. The spine is a frequent site of bone metastasis. Vertebral osteomyelitis is uncommon at roughly 1 per 100,000 persons annually, with rising rates attributed to vascular devices and intravenous drug use; it occurs more often in early childhood and in adults over 50. Spinal epidural abscess occurs in about 1 per 10,000 hospital admissions per year, and MRSA-related vertebral osteomyelitis and epidural abscess are increasingly reported. Despite global increases in tuberculosis, the rate of extrapulmonary spinal disease remains relatively stable; Pott disease, typically involving the lower thoracic vertebrae, is the most common musculoskeletal extrapulmonary manifestation. Improved survival in sickle cell disease has been accompanied by more Salmonella vertebral osteomyelitis.
Risk Factors
Infectious complications can follow bites from many animals, often linked to occupational exposure (farmers, laboratory workers, veterinarians) or recreation (hunters, campers, exotic pet owners). Systemic infection after animal or human bites is more likely with extremity edema or impaired lymphatic drainage and in immunocompromised hosts. Fever after a dog bite in an immunosuppressed patient should prompt concern for invasive Capnocytophaga canimorsus infection.
Etiology
Infectious sources of back pain with fever include biliary tract infection, chronic prostatitis, herpes zoster, pyelonephritis, retroperitoneal abscess, spinal epidural abscess, and vertebral osteomyelitis. Noninfectious causes include colonic cancer, pancreatic disease, histiocytosis X, metastatic malignancy (breast, lung, prostate, thyroid, kidney, gastrointestinal tract), multiple myeloma, neoplastic invasion of pelvic nerves, lymphoma, pregnancy, vertebral fracture, renal artery or vein thrombosis, renal stones, retroperitoneal hemorrhage or tumors, and tumors of the posterior stomach or duodenum. Staphylococcus aureus is the leading cause of spinal epidural abscess, accounting for most reported cases, with additional pathogens including Actinomyces israelii, Aspergillus, Blastomyces, Brucella, Cryptococcus, Haemophilus parainfluenzae, Mycobacterium tuberculosis, and Streptococcus milleri. Vertebral osteomyelitis is most often due to staphylococci but may be caused by other bacteria or tuberculosis; one multicenter retrospective study from southern Spain reported a high proportion due to Brucella, with the remainder split between pyogenic and tuberculous disease.
Commonly Associated Conditions
Vertebral osteomyelitis and spinal epidural abscess are frequently associated with diabetes, injection drug use, chronic renal failure, alcohol use disorder, bacteremia or focal infections, and malignancy. Most epidural abscesses arise via hematogenous spread from skin or mucosal sources, though direct extension from adjacent infection is also recognized. Postoperative abscesses account for a substantial minority, and epidural catheter placement is another risk factor. Blunt trauma may precede symptoms and may lead to an epidural hematoma that later becomes infected.
Diagnosis
Spinal epidural abscess classically presents with fever, spinal pain and tenderness, and radicular pain progressing to limb weakness, with pain being the most consistent feature. Early on, spinal pain with or without fever may be the only findings before sudden neurologic decline. When sepsis dominates or when patients are bedbound, neurologic deficits may be missed. Fever is absent in a notable minority of pyogenic vertebral osteomyelitis cases and is even more commonly absent in tuberculous vertebral osteomyelitis.
History
Key elements include age; systemic symptoms such as fever, weakness, weight loss, and night sweats; prior trauma, infection, or cancer; pain characteristics; immune status; glycemic control in diabetes; and injection drug use. Screen for neurologic complaints including weakness, paresthesias, numbness, and bowel, bladder, or sexual dysfunction. Risk is higher in patients over 50, those using steroids, individuals with HIV, those on immunosuppressants, and those with prior surgery.
Physical Examination
Assess general appearance, vital signs, peripheral pulses, and perform a focused cardiopulmonary and abdominal evaluation in unstable patients. Look for referred pain by examining potential primary sources of tenderness. Perform a complete neurologic examination to evaluate for spinal cord compromise and localize deficits; lesions below T12 can produce lower motor neuron findings, and cauda equina syndrome may include bowel or bladder incontinence. In older adults, fever may be low-grade and does not reliably indicate severity. Percussion of spinous processes may reveal focal vertebral tenderness due to trauma, malignancy, or infection. Examine for signs of endocarditis and septic emboli.
Diagnostic Tests and Interpretation
Laboratory Studies
Routine blood tests are often nonspecific for vertebral osteomyelitis, but leukocytosis, neutrophilia, and markedly elevated ESR and C-reactive protein support pyogenic disease. Blood cultures are the most useful routine test and identify the organism in about half of pyogenic and Brucella vertebral osteomyelitis cases. Bone biopsy is often required to confirm the diagnosis, especially in tuberculous disease.
Imaging
Plain spinal radiographs may be normal early in vertebral osteomyelitis. MRI best defines the extent and location of spinal epidural abscess. MRI or CT myelography is preferred when spinal metastasis is suspected.
Diagnostic Procedures/Other
CT-guided needle biopsy reliably diagnoses carcinoma but is less dependable for lymphoma, though performance has improved with CT guidance, immunophenotyping, and larger needles; false-negative rates remain significant. Establishing an etiologic diagnosis of vertebral osteomyelitis often requires percutaneous or surgical vertebral biopsy.
Differential Diagnosis
Tuberculosis may appear early as an opportunistic infection in AIDS and can be AIDS-defining, while Mycobacterium avium complex typically occurs later with very low CD4 counts. Pertussis should be considered when cough is the predominant symptom, particularly with paroxysms, inspiratory whoop, posttussive vomiting, sleep-disrupting cough, or exposure to similar illness.
Treatment
Medications
Suspected vertebral osteomyelitis or epidural abscess warrants empiric vancomycin to cover MRSA, with addition of a third- or fourth-generation cephalosporin when gram-negative bacteremia is suspected, especially with concurrent pyelonephritis. Therapy should be narrowed once the pathogen is identified; for methicillin-sensitive S. aureus, options include nafcillin, oxacillin, or cefazolin. Typical duration is at least six weeks. Management of tuberculous, brucellar, and salmonella bone disease follows their respective regimens. Corticosteroids may help in acute spinal cord compression. NSAIDs provide symptomatic analgesia, and bisphosphonates may be used for fractures related to breast cancer metastases.
Additional Treatment
Prompt diagnosis with targeted therapy is essential. Epidural abscess requires urgent surgical management with early decompression plus antibiotics. Spinal cord compression is a neurosurgical emergency, and decompression via surgery or radiotherapy within 24 hours of symptom onset is needed to reduce permanent neurologic injury. In suspected spinal or paraspinal infection, bactericidal empiric antibiotics should be started immediately.
.
Ongoing Care and Follow-Up
If symptoms persist beyond six weeks, repeat laboratory testing and imaging are recommended. After six weeks of antibiotics for osteomyelitis or epidural abscess, reassessment is needed to determine whether treatment should continue. Ongoing monitoring for medication toxicity is important, particularly in older adults who are more susceptible to adverse drug effects.
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