What is Baastrup’s disease (kissing spine syndrome) and how is it diagnosed and managed?

Baastrup's Disease (Kissing Spine Syndrome)

Definition and Clinical Presentation

Baastrup's disease is a degenerative spinal condition characterized by close approximation and contact of adjacent spinous processes, most commonly affecting L4-L5, causing midline low back pain that worsens with extension and improves with flexion. 1, 2

The condition typically presents with:

• Midline low back pain exacerbated by spinal extension and relieved by flexion 1, 3
• Point tenderness upon direct finger pressure over the affected spinous processes 1, 3
• Higher occurrence in patients over 70 years of age, though cases occur in younger adults 1, 2
• No gender predilection (male-to-female ratio approximately 1.3:1) 2
• Decade-on-decade increase in incidence based on population studies 2

Pathophysiology

The underlying mechanism involves:

• Excessive lumbar lordosis producing mechanical pressure and repetitive strain on the interspinous ligament 1
• Progressive degeneration and collapse of the interspinous ligament 1
• Development of secondary changes including edema, sclerosis, flattening and enlargement of articulating spinous process surfaces, bursitis, and occasionally epidural cysts or midline epidural fibrotic masses 1

Diagnostic Approach

Clinical Examination

The diagnosis requires both clinical suspicion based on characteristic pain patterns and confirmation with imaging studies. 1, 2

Key examination findings include:

• Midline tenderness at the level of interest 1, 3
• Pain reproduction with spinal extension 1, 3
• Pain relief with spinal flexion 1, 3

Imaging Studies

Standard and dynamic flexion-extension radiographs of the lumbar spine should be the initial imaging modality, as they demonstrate the characteristic close approximation of spinous processes and can reveal dynamic changes. 2

MRI is the most comprehensive imaging modality, identifying not only the kissing spinous processes but also secondary findings including flattening, sclerosis, enlargement, cystic lesions, bone edema, and bursitis at the articulating surfaces. 1, 2, 4

CT scan provides excellent visualization of bony changes including sclerosis, flattening, and enlargement of spinous processes. 2

FDG-PET/CT can detect active inflammation or bursitis even when MRI and bone scan are negative, and is particularly useful for identifying the exact site of inflammation in multilevel vertebral involvement to guide targeted injections. 2, 4

Imaging Protocol Recommendations

Based on the available evidence:

1. Begin with standard anteroposterior and lateral radiographs of the lumbar spine 2
2. Add dynamic flexion-extension views to assess for movement-related changes 2
3. Proceed to MRI when radiographs are suggestive or when soft tissue pathology (bursitis, epidural cysts) needs evaluation 1, 2
4. Consider FDG-PET/CT when MRI is negative but clinical suspicion remains high, or when precise localization is needed for injection therapy in multilevel disease 2, 4

Common Diagnostic Pitfalls

Baastrup's disease is overwhelmingly underdiagnosed due to lack of knowledge and improper diagnostic techniques, leading to frequent mistreatment. 3

Clinicians often resort to MRI without obtaining dynamic flexion-extension radiographs, which can miss the diagnosis when soft tissue changes are minimal. 2

In cases with strong clinical suspicion but unclear radiological findings, diagnostic/therapeutic injection can provide both confirmation and symptom relief. 5

Management

Conservative Treatment

Anti-inflammatory drugs and physical therapy are appropriate first-line treatments, used in approximately 36% of reported cases. 2

Conservative measures include:

• NSAIDs for pain control 2
• Physical therapy focusing on flexion-based exercises 2
• Activity modification to avoid prolonged extension 1

Interventional Treatment

Percutaneous steroid infiltrations into the interspinous space or bursa provide targeted anti-inflammatory therapy and are used in approximately 29% of cases. 2, 3

FDG-PET/CT can identify the exact site of inflammation where steroid or local anesthetic injection should be administered, especially in patients with multilevel vertebral involvement. 4

The injection approach:

• Subcutaneous or interspinous steroid injection at the site of maximal tenderness and imaging-confirmed pathology 3
• Can provide considerable clinical improvement 3
• May serve as both diagnostic confirmation and therapeutic intervention 5

Surgical Treatment

Surgical decompression (excision of the bursa, partial spinous process resection, or osteotomy) is reserved for refractory cases and was performed in approximately 71% of reported surgical series. 1, 2

Surgical indications include:

• Failure of conservative and injection therapies 2, 5
• Persistent disabling pain despite adequate conservative management 5
• Presence of epidural cysts or significant epidural fibrotic masses causing neurological symptoms 1

Surgical management can allow return to normal social and professional life in appropriately selected patients. 5

Treatment Algorithm

1. Begin with NSAIDs and physical therapy for 6-12 weeks 2
2. If symptoms persist, proceed to image-guided steroid injection 2, 3, 4
3. Reserve surgical decompression for patients who fail conservative and injection therapies 2, 5

Evidence Gaps

There is a critical need for randomized clinical trials comparing conservative, interventional, and surgical therapies, as current treatment recommendations are based primarily on case series and retrospective studies. 2