An unusual case of paraparesis due to hypertrophy of posterior longitudinal ligament at thoracic and lumbar spine with long-term follow-up: a case report and literature review.

introductionHypertrophy of the posterior longitudinal ligament (HPLL) is a rare cause of spinal cord compression, most commonly affecting the cervical spine. Thoracic and lumbar involvement are exceptional, and the natural history of HPLL, particularly its relationship to ossification of the PLL (OPLL), remains unclear. To our knowledge, this is the first reported case of diffuse thoracolumbar HPLL presenting with unusual features and showing no ossification at long-term follow-up. CASE PRESENTATION: We present a 50-year-old man with rapidly progressive paraparesis and gait disturbance. Imaging revealed a continuous, non-ossified, intraspinal, ventral lesion from T5 to L4, with severe cord compression at T10-L1, hypointense signaling on T1W and T2W images, and progression compared with the MRI performed 7 years earlier, suggestive of HPLL. The patient underwent anterior T10-L1 HPLL resection with fusion and posterior L1-L3 decompression, resulting in full neurological recovery. Histopathology demonstrated hyalinized collagenous tissue with chronic inflammatory infiltrates. After 13 years of follow-up, the patient remained ambulatory, with imaging showing persistent non-ossified HPLL in the thoracic and lumbar unresected regions, no recurrence at the resected region, and new thoracic anterior longitudinal ligament hypertrophy (HALL). DISCUSSION: This case illustrates a rare form of diffuse thoracolumbar HPLL with long-term stability and no transition to ossification, suggesting distinct biological pathways for HPLL and OPLL with the additional novel finding of HALL. The presence of chronic inflammation supports a potential role for inflammation-driven fibrosis in ligamentous hypertrophy. Tailored surgical strategies and vigilant long-term follow-ups are essential in managing HPLL.