Earliest Radiographic Findings of DISH and Location of Onset
The earliest radiographic findings of DISH are flowing ossification along the anterior and anterolateral aspects of the thoracic spine, most commonly beginning in the middle and lower thoracic regions (T6-T10), with initial involvement typically affecting just a few contiguous vertebrae before extending cranially and caudally.
Initial Location and Pattern
DISH characteristically begins in the mid to lower thoracic spine 1, 2. The disease rarely starts in the upper thoracic region 1. The initial presentation involves:
- A few vertebrae first affected (typically 2-3 contiguous levels)
- Progressive extension that can eventually span the entire thoracic spine
- Predominantly right-sided ossification in early stages, becoming more circumferential over time 2
The thoracic region shows the highest propensity for complete fusion compared to lumbar segments, with the upper and lower thoracic regions demonstrating the most dynamic changes during disease progression 2.
Earliest Radiographic Features
Primary Findings
The hallmark early finding is flowing ossification along the anterior and anterolateral vertebral bodies 1, 3. This presents as:
- Vertical hyperostosis spanning the anterior aspects of vertebrae
- Thickness varying up to 10mm
- Characteristic "dripping candle wax" appearance 4
- Preserved intervertebral disc height (critical distinguishing feature) 3
Stage 1 Characteristics
In the earliest phase (Stage 1), radiographic measurements show 2:
- Partial calcification of disc spaces (38% of disc spaces show at least partial involvement)
- Osteophyte growth rate of approximately 10.89mm²/year
- Increasing linear attenuation coefficient (17.04 HU/year), indicating active bone formation
- Predominantly anterior and right-sided location
Diagnostic Criteria Application
While formal DISH diagnosis requires flowing ossification of at least 4 contiguous vertebrae 3, 5, recognizing early-phase DISH with fewer involved segments is clinically important. The complete diagnostic criteria include:
- Flowing ossification along ≥4 contiguous vertebrae
- Preserved disc height
- Absence of facet joint ankylosis
- No sacroiliac joint erosions or ankylosis 3
Clinical Context
Demographics
- Male predominance (12:1 male-to-female ratio in some studies) 1
- Most common in 6th-7th decades of life 3
- Prevalence of 5-15% in elderly populations 3
Associated Findings
Early DISH frequently coexists with 2:
- Extraspinal enthesopathies (ankles, pelvis, knees most common) 6
- Reduced vertebral bone density 7
- Metabolic associations (though diabetes/hypertension correlations are inconsistent) 1, 8
Imaging Modality Considerations
Conventional radiography remains the first-line imaging modality 9, 3. However:
- CT provides superior detection of subtle early ossifications and better delineates complex anatomy 3
- MRI has limited sensitivity (32-44%) for detecting DISH ossifications 10
- CT is particularly valuable for identifying early enthesitis-related bone production in posterior elements 11
Common Pitfalls
Distinguishing from ankylosing spondylitis: DISH affects anterior/anterolateral spine with preserved disc spaces and no sacroiliac involvement, while AS shows posterior element fusion and sacroiliitis 1
Artifact on DXA scans: DISH causes spuriously elevated bone mineral density readings and should prompt vertebral exclusion when T-score differences exceed 1.0 between adjacent vertebrae 9
Delayed recognition: The disease progresses slowly—estimated 17.96 years from onset to complete thoracolumbar ankylosis 2—making early detection challenging
Clinical significance: Even early DISH increases spinal fracture risk and associates with metabolic syndrome, coronary disease, and respiratory effects 8, 5
The natural history shows that after initial mid-lower thoracic involvement, the disease extends both cranially and caudally over years to decades, with the thoracic region showing the greatest tendency toward complete fusion 1, 2.