Correct Answer: A. Ankylosing spondylitis
Ankylosing spondylitis (AS) is a seronegative spondyloarthropathy characterized by the clinical triad presented here: early morning backache with stiffness that improves on exercise (inflammatory back pain pattern), extra-articular manifestations (persistent red eyes = acute anterior uveitis), and restricted chest expansion (<3 cm, normal >5 cm). The X-ray showing "bamboo spine" (continuous ossification of spinal ligaments creating a rigid column) is pathognomonic for advanced AS. The disease predominantly affects young males (male:female = 3:1) and is strongly associated with HLA-B27 positivity (>90% in Indian populations). The inflammatory back pain improves with activity and NSAIDs, distinguishing it from mechanical back pain. Reduced lung expansion occurs due to costovertebral joint fusion and thoracic spine rigidity, leading to restrictive lung disease. Uveitis occurs in 25–30% of AS patients and is often the presenting feature. The combination of inflammatory spinal disease, uveitis, and characteristic radiological findings makes AS the definitive diagnosis.
Why the other options are wrong
B. Healed tuberculosis — Healed TB causes kyphotic deformity and anterior vertebral body collapse (Pott's disease sequelae), not continuous ossification of ligaments. TB does not produce bamboo spine or cause uveitis. The clinical presentation of inflammatory back pain improving with exercise is incompatible with TB sequelae, which cause mechanical pain worse with activity. Reduced lung expansion in TB is from parenchymal fibrosis, not costovertebral fusion. C. Osteopetrosis — Osteopetrosis is a rare genetic disorder of osteoclast dysfunction causing generalized increased bone density (marble bone appearance on X-ray), not ligamentous ossification. It presents in childhood with pancytopenia, hepatosplenomegaly, and cranial nerve compression—not in young adults with inflammatory back pain and uveitis. The radiological pattern of bamboo spine is entirely different from the uniform hyperdensity seen in osteopetrosis. D. Paget's disease — Paget's disease causes focal areas of abnormal bone remodeling with mixed lytic and sclerotic lesions, typically in pelvis, femur, and skull—not diffuse spinal ligamentous ossification. It presents in elderly patients (>40 years) with bone pain and deformity, not in young men with inflammatory back pain. Paget's does not cause uveitis or the characteristic bamboo spine pattern seen on X-ray.
High-Yield Facts
- Inflammatory back pain in AS: morning stiffness >30 minutes, improves with exercise, worse in second half of night—distinguishes from mechanical back pain.
- HLA-B27 association: present in >90% of AS patients in Indian populations; negative HLA-B27 does not exclude AS but makes diagnosis less likely.
- Bamboo spine: continuous ossification of spinal ligaments (anterior longitudinal ligament, interspinous ligaments) creating rigid column—pathognomonic radiological finding.
- Reduced chest expansion: normal >5 cm; AS causes <3 cm due to costovertebral joint fusion and thoracic spine rigidity, leading to restrictive lung disease.
- Acute anterior uveitis: occurs in 25–30% of AS patients; recurrent, unilateral, painful with photophobia—requires urgent ophthalmology referral.
- Male predominance: AS affects males 3 times more than females; typically presents in 2nd–3rd decade.
- NSAIDs as first-line: indomethacin 75–100 mg/day is DOC for AS; TNF-α inhibitors (infliximab, adalimumab) for DMARD-resistant cases in India.
Mnemonics
ASAS Criteria for AS (Simplified) Acute anterior Uveitis, Sacroiliitis on imaging, Ankylosed spine, Seronegative (RF/anti-CCP negative). Remember: AS = Anterior uveitis + Ankylosed spine + Seronegative. IBP vs Mechanical Back Pain IBP (AS): Improves with exercise, Inflammatory (morning stiffness >30 min), In young males. MBP: Mechanical (worse with activity), Middle-aged/elderly, Morning stiffness <30 min. Chest Expansion Rule Normal >5 cm, AS <3 cm, Borderline 3–5 cm. Use tape measure at 4th intercostal space during full inspiration–expiration.
NBE Trap
NBE may pair "healed TB" with "kyphotic deformity" to trap students who confuse Pott's disease sequelae (vertebral collapse, kyphosis) with AS (ligamentous ossification, bamboo spine). The key discriminator is that TB causes focal collapse and deformity, while AS causes diffuse, continuous spinal rigidity with preserved vertebral body height.
Clinical Pearl
In Indian clinical practice, AS is often missed because patients present first to orthopedics or pulmonology with back pain or reduced lung function. Always ask young males with "morning back stiffness that improves with exercise" about red eyes and check HLA-B27 and sacroiliac imaging (X-ray or MRI)—early diagnosis and NSAIDs can prevent spinal fusion and disability.
_Reference: Harrison Ch. 324 (Ankylosing Spondylitis); Robbins Ch. 26 (Seronegative Spondyloarthropathies); Park's Textbook of Preventive and Social Medicine (epidemiology of AS in India)_