Diffuse Idiopathic Skeletal Hyperostosis (DISH) is a systemic, non-inflammatory disease characterized by abnormal calcification and ossification of ligaments and entheses, most notably along the spine. Initially termed "senile ankylosing hyperostosis" by Forestier and Rotes-Querol in 1950, DISH became widely recognized through the diagnostic criteria established. The pathognomonic feature of DISH is the flowing ossification along the anterolateral aspect of at least three or four contiguous vertebral bodies, typically sparing the sacroiliac and apophyseal joints, which sharply distinguishes it from other conditions like ankylosing spondylitis (AS) and degenerative osteoarthritis.[1] Although most cases are asymptomatic and discovered incidentally, clinical manifestations can range from mild spinal stiffness to severe complications such as restricted motility or even dysphagia when cervical vertebrae are involved. The prevalence of DISH is higher in males over 50 years of age and is strongly associated with metabolic conditions such as diabetes, obesity, hyperlipidemia, and hyperuricemia. Genetic predispositions, such as HLA-B8, have also been implicated, especially given its overlap with diabetes mellitus. The precise etiology, however, remains poorly understood, and there is no clear association with HLA-B27, which is frequently found in seronegative spondyloarthropathies.[2] Radiologically, DISH is defined by characteristic bony bridges extending over several vertebral levels, with relative preservation of disc height, and a lack of degenerative disc disease or significant facet joint ankylosis. These features can make DISH challenging to differentiate from spondyloarthropathies, particularly in elderly patients presenting with chronic back pain and spinal stiffness. However, the absence of sacroiliac joint erosions, sclerosis, or osseous fusion, and the unique “candle-wax” appearance of anterior bridging in DISH, contrast with the sacroiliitis and smooth bony bridging seen in AS.[3] DISH can coexist with other spinal disorders, and diagnosis often relies on a careful integration of clinical, laboratory, and radiological findings. Misdiagnosis as spondyloarthropathy remains a significant risk due to the overlap in clinical presentation, particularly spinal stiffness, and radiological findings such as syndesmophytes. Conventional radiography remains the gold standard for identification, with confirmation via computed tomography (CT) or magnetic resonance imaging (MRI) in ambiguous cases.[4] There is currently no cure for DISH, and management is primarily conservative, focusing on symptomatic relief and the prevention of complications. Physical therapy, analgesics, and, rarely, surgical interventions for severe spinal cord compression or dysphagia may be indicated. The differentiation from spondyloarthropathies has significant therapeutic and prognostic implications, as disease-modifying antirheumatic drugs (DMARDs) typically used for spondyloarthritis are not effective in DISH.[5] In this case report, we describe a patient with DISH whose clinical and radiological features closely mimicked spondyloarthropathy, highlighting the importance of careful imaging and diagnostic correlation to achieve an accurate diagnosis and appropriate management. Aim To describe a case of Diffuse Idiopathic Skeletal Hyperostosis (DISH) presenting with clinical and radiological features mimicking spondyloarthropathy. Objectives • To document the clinical profile and radiological findings of DISH in a patient initially suspected of spondyloarthropathy. • To compare and contrast the imaging characteristics and diagnostic criteria of DISH and spondyloarthropathies. • To underscore the importance of appropriate diagnostic workup in differentiating DISH from spondyloarthropathy for optimal patient management.

Source of Data Retrospective analysis was performed on the clinical records and radiological investigations of a single patient evaluated at the Rheumatology Department of Nizam’s Institute of Medical Sciences. Study Design This study was a case report with radiological correlation. Study Location The study was conducted in the Rheumatology outpatient clinic at Nizam’s Institute of Medical Sciences, Hyderabad, India. Study Duration The patient’s medical records spanning from 2012 to 2020 were reviewed. Inclusion Criteria • Patient diagnosed with DISH based on Resnick criteria. • Complete clinical and radiological data available for correlation. • Age above 40 years. Exclusion Criteria • Incomplete medical or radiological records. • Unclear differentiation between DISH and primary spondyloarthropathy. • Patients with metastatic spinal disease or severe infection. Procedure and Methodology The case details were extracted systematically from patient files, including presenting symptoms, duration, and physical examination findings. Radiological investigations (X-ray, CT, MRI) were thoroughly reviewed. Diagnosis of DISH was based on established criteria including flowing ossification along the anterolateral aspect of at least four contiguous vertebral bodies, preservation of intervertebral disc height, and absence of significant facet joint ankylosis or sacroiliac fusion. Differential diagnosis with spondyloarthritis was considered as per radiological and clinical findings. Sample Processing Radiological images were independently reviewed and correlated with symptoms. Laboratory investigations including ESR, CRP, and HLA-B27 status were noted and assessed in context. Statistical Methods As this is a case report, descriptive statistics (mean, ranges) were used where applicable. Tabulation of clinical findings and radiological features was performed for clarity. Data Collection Data were collected retrospectively from electronic medical records and patient charts. Imaging findings were correlated with clinical history to validate the diagnosis.

Table 1: Case Description – DISH Presenting as Spondyloarthropathy Parameter Description Age/Sex 53 years/Male Symptoms Gradual-onset low back pain, bilateral thigh pain, stiffness Duration Symptoms >15 years, worsened last 15 days Past Treatment On xyfor/rheumatology meds, off tablets post-COVID Clinical Findings Waddling gait, short steps, severe paraspinal spasm, no effusion/enthesitis Neurological Signs Absent; no focal deficit or bladder involvement Laboratory Tests HLA-B27 negative, no raised CRP/ESR Radiology Flowing ossification anterior longitudinal ligament (multiple vertebrae), bridging syndesmophytes, preserved disc height, absence SIJ erosions/fusion Final Impression DISH mimicking spondyloarthropathy Table 1 describes the case of a 53-year-old male patient who presented with a longstanding history of gradual-onset low back pain, bilateral thigh pain, and stiffness, with symptoms persisting for more than 15 years and a recent worsening in the last 15 days. The patient had previously been on medications for rheumatological issues, discontinued after COVID, and exhibited clinical findings including waddling gait, short steps, severe paraspinal spasm, but no effusion or enthesitis. Importantly, no neurological deficits or bladder involvement were noted. Laboratory tests revealed HLA-B27 negativity and normal CRP/ESR values. Radiological investigations documented flowing ossification of the anterior longitudinal ligament across multiple vertebrae, bridging syndesmophytes, and preserved disc height without sacroiliac joint erosions or fusion-all features highly consistent with DISH, though initially mimicking spondyloarthropathy. Table 2: Clinical and Radiological Profile in Patient Initially Suspected Spondyloarthropathy Aspect Finding (Index Case) Initial Suspect Ankylosing spondylitis/spondyloarthropathy Key History Chronic low back pain, insidious onset stiffness, no enthesitis or peripheral arthritis Physical Exam Spinal stiffness, loss of lumbar lordosis, waddling gait Laboratory Workup HLA-B27 negative, normal inflammatory markers Imaging Spine Flowing anterior vertebral ossifications on X-ray/MRI SIJ Views No SIJ fusion, no erosions Additional Enthesophytes in pelvis, hypertrophic changes, cord edema (MRI) Clinical Evolution Non-progressive neurological status; suspicion revised to DISH Table 2 outlines the clinical and radiological profile of the patient who was initially suspected to have ankylosing spondylitis or another spondyloarthropathy. The patient’s history included chronic low back pain and insidious onset stiffness without enthesitis or peripheral arthritis. Physical examination revealed spinal stiffness, loss of lumbar lordosis, and waddling gait. Laboratory workup continued to show normal inflammatory markers and HLA-B27 negativity. Imaging studies identified flowing anterior vertebral ossifications without sacroiliac joint fusion or erosions. Additional radiological findings included pelvic enthesophytes, hypertrophic changes, and MRI evidence of cord edema. The clinical course was marked by non-progressive neurological status, leading to a revised diagnosis of DISH rather than spondyloarthropathy. Table 3: Imaging and Diagnostic Criteria – DISH vs Spondyloarthropathy Feature DISH Spondyloarthropathy Spinal Changes Flowing ossification (>4 vertebrae) Marginal/bony bridging syndesmophytes Disc Spaces Preserved Reduced in advanced disease SI Joint Involvement Absent Frequently fused/eroded Facet Joint Ankylosis Absent/minimal Present in advanced cases Enthesophytes/Extra-spinal Common Uncommon HLA-B27 Association Absent Common Inflammatory Markers Normal Often raised Table 3 provides a comparative summary of the imaging and diagnostic criteria distinguishing DISH from spondyloarthropathy. DISH is characterized by flowing ossification over more than four contiguous vertebrae, preserved disc spaces, and absent sacroiliac and facet joint involvement, with common extra-spinal enthesophytes. In contrast, spondyloarthropathy typically exhibits marginal syndesmophytes, disc space reduction in advanced stages, frequent sacroiliac joint fusion or erosion, facet joint ankylosis, uncommon extra-spinal enthesophytes, a strong association with HLA-B27, and often raised inflammatory markers. Table 4: Importance of Diagnostic Workup in DISH vs Spondyloarthropathy Component Diagnostic Role Impact on Management Detailed Clinical History Identifies symptom pattern, chronicity, absence of true inflammatory features Prevents unwarranted immunosuppressive therapy HLA-B27/Serology Differentiates from spondyloarthritis Guides further workup, avoids misdiagnosis Radiological Assessment Shows classic flowing ossification, preserved SIJ/disc, differentiates DISH Reduces unnecessary imaging and inappropriate therapy MRI/Advanced Imaging Detects cord compression, excludes enthesitis or marrow edema Supports safe, targeted interventions Multidisciplinary Review Ensures accuracy ex. neurologic assessment in cord compromise Optimizes patient outcomes Table 4 highlights the importance of a comprehensive diagnostic workup for discriminating between DISH and spondyloarthropathy. A detailed clinical history is critical to recognizing symptom chronicity and the absence of true inflammatory features, which helps avoid inappropriate use of immunosuppressive therapies. HLA-B27 testing and inflammatory marker assessment further support differentiation. Radiological assessment is essential to demonstrate hallmark features of DISH-such as flowing ossification with preserved disc and SI joint integrity-thus preventing misdiagnosis. MRI and advanced imaging can detect cord compression and rule out enthesitis, guiding safe, patient-centered intervention.

The case presented in Table 1, describing a 53-year-old male with longstanding gradual-onset low back pain, bilateral thigh pain, and stiffness, parallels findings from other studies where DISH typically manifests in middle-aged to elderly males with chronic, often mild, back symptoms. Our patient's clinical features including waddling gait and paraspinal spasm without neurological deficits align with the often insidious and non-inflammatory presentation of DISH Liao S et al.(2025)[6]. The absence of HLA-B27 and inflammatory markers further supports the diagnosis, as confirmed by flowing ossification along the anterior longitudinal ligament spanning multiple vertebrae, a hallmark radiological feature distinguishing DISH from spondyloarthropathies. This clinical-radiological pattern is consistent with previous case reports where DISH mimicked spondyloarthropathies but lacked sacroiliac joint involvement or raised inflammatory markers. Table 2 highlights the diagnostic dilemma encountered when this patient was initially suspected to have ankylosing spondylitis (AS) or related spondyloarthropathy. Chronic back pain with stiffness and spinal restriction are shared features in DISH and AS, complicating differentiation in clinical practice. However, the radiological absence of sacroiliac joint fusion or erosions and preservation of disc height, coupled with the presence of bulky bridging osteophytes, favored DISH diagnosis, a finding supported by Tripathi M et al.(2020)[7] who stressed the importance of imaging in differential diagnosis. Additional MRI findings of cord edema, while rare, have been described in complicated DISH cases involving neurological compression Gazel U et al.(2024)[8]. The non-progressive neurological status and absence of peripheral arthritis further contested an AS diagnosis, aligning with the milder symptomatology typically seen in DISH. In Table 3, classic imaging and diagnostic features are compared between DISH and spondyloarthropathies, such as AS. The flowing ossification in more than four contiguous vertebrae with minimal disc involvement contrasts with marginal syndesmophytes and disc space narrowing in AS, reiterating criteria widely reported in the literature. Sacroiliac joint sparing in DISH versus frequent involvement in spondyloarthropathies remains a critical differentiator, although recent studies warn that sacroiliac abnormalities may occasionally be seen in DISH, complicating distinction further. Moreover, the lack of HLA-B27 association and normal inflammatory markers in DISH provides a biochemical basis for clinical differentiation from spondyloarthropathies. Tanios M et al.(2023)[9] Table 4 emphasizes the clinical utility of a comprehensive diagnostic approach, echoing prior research advocating for multidisciplinary evaluation in such cases. Detailed history-taking and serological testing prevent unnecessary immunosuppressive treatments used in spondyloarthropathies, while radiological assessments focusing on classic DISH features guide appropriate diagnosis and management. Advanced imaging modalities like MRI play a vital role in identifying rare neurological complications, further supporting safe interventions. Multidisciplinary review, involving rheumatology, radiology, and neurology, ensures accurate diagnosis, optimizing patient outcomes-the consensus approach recommended in recent expert reviews. Aps JK et al.(2021)[10]

This case report highlights the diagnostic challenge of Diffuse Idiopathic Skeletal Hyperostosis (DISH) mimicking spondyloarthropathy due to overlapping clinical and radiological features. In this 53-year-old male patient, the presence of chronic low back pain, spinal stiffness, and flowing ossification on imaging initially suggested spondyloarthropathy, but detailed evaluation revealed characteristic features of DISH, including absent sacroiliac joint involvement, negative HLA-B27, and normal inflammatory markers. Careful clinicoradiological correlation and multidisciplinary assessment were pivotal in reaching the correct diagnosis, avoiding inappropriate immunosuppressive therapy and guiding suitable management. This case underscores the importance of distinguishing DISH from spondyloarthropathies to optimize patient care and outcomes. LIMITATIONS As a single case report, generalizability of findings is limited. The retrospective nature restricted prospective follow-up and systematic evaluation of treatment response. Imaging and laboratory investigations were dependent on available clinical data without standardized protocols for differentiation. The absence of biopsy or advanced biomarker analysis limits mechanistic insights into the pathological overlap or distinctiveness of DISH and spondyloarthropathy. Larger prospective studies with comprehensive diagnostic workups are needed to better elucidate clinical and radiological distinctions and optimize diagnostic algorithms.

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