HPLL-induced cervical cord myelopathy - a case report

Clinical History

A 38-year-old patient came with the history of slowly progressive bilateral upper and lower limb weakness. She was referred for MRI of the cervical spine. CT sections through the cervical spine were also carried out.

Imaging Findings

• On T1 weighted sagittal images there is evidence of thickening of posterior longitudinal ligament, the tectorial membrane, the ligamentum flavum and the supraspinous ligament from the level of foramen magnum up to the C6 level which appear isointense. On the T2 weighted sagittal images, the ligamentous thickening is well demonstrated as uniform low signal intensity. The supraspinous ligamentous thickening is also well seen.
• The cervical cord from the level of cranio- vertebral junction to C2 level appears compressed especially behind the peg and shows mild hyperintensity - Cervical cord myelopathy secondary to compression by the thickened ligaments.
• On the CT sections there was no evidence of ossification seen to either thickened posterior longitudinal ligament or the ligamentum flavum.

Discussion

The case report is presented from Nalgonda district of Andhra Pradesh. It is a known endemic region for fluorosis due to high fluoride content in water because of native rock composition. Safe and adequate intake of fluoride is 1.5 to 4 mg/day. The daily intake of fluoride in endemic areas varies from 10 to 35 mg [1]. In our patient serum fluoride level was elevated.
The main manifestations of fluoride intoxication are dental and skeletal fluorosis [2].
Characteristic radiological findings of fluorotic spine includes sclerotic bone, osteophyte formation, thickening of ligaments with further progression to ossification [1].The density rise is quantitative rather than qualitative owing to increase in matrix unaccompanied by any increase in mineralization. Bone continues to form as the thickened trabeculae with uncalcified borders are resistant to resorption and therefore they thicken [10]. Thickening of ligaments with further ossification is seen. The ligaments mainly involved are posterior longitudinal ligament and ligamentum flavum resulting in compressive myelopathy. Hypertrophy of the posterior longitudinal ligament was first described by Kamikozuru et al in 1974. Thickening of posterior longitudinal ligament (PLL) greater than 3.5 mm in anteroposterior diameter is considered as HPLL [6]. Thickening of tectorial membrane is seen. The mean thickness of this membrane is about 1 mm [9]. Cervical spinal cord involvement is common followed by thoracic and lumbar region. MRI and Computed Tomography are useful in establishing diagnosis of HPLL [3]. Hypertrophy of posterior longitudinal ligament is a prodromal condition to ossification [4]. MRI delineates soft tissue structures and changes in the spinal cord. Fluorotic vertebrae appear hypointense on both T1 and T2 weighted sequences [10]. However, in our case, fluorosis was picked up early before its progression into next stage of ossification of ligaments and increase in bone density. Early diagnosis of hypertrophy of posterior longitudinal ligament before its ossification is important as it may aid in prompt therapy. Surgical treatment with anterior decompression can be performed in HPLL at an early stage in order to prevent deterioration and obtain neurological improvement [7]. Patients with HPLL can benefit from an anterior approach with direct removal of the HPLL [3]. The treatment option for ossified posterior longitudinal ligament includes techniques like laminoplasty, laminectomy, and laminectomy with instrumented fusion [8]. The average recovery rate was significantly higher in cases of HPLL as compared to OPLL. Hence early diagnosis is important [5].

Differential Diagnosis List

Final Diagnosis

Hypertrophic Posterior Longitudinal Ligament induced cervical cord myelopathy in a fluorotic patient

URL:	https://www.eurorad.org/case/11447
DOI:	10.1594/EURORAD/CASE.11447
ISSN:	1563-4086