Compressive Myelopathy Secondary to Atlantoaxial Dislocation in a Child with Congenital Hypothyroidism: A Case Report.

Atlantoaxial dislocation (AAD) occurs secondary to joint laxity between C1 and C2 vertebrae, resulting in loss of normal articulation and movement. Etiology of AAD could be genetic, inflammatory, or rarely traumatic. Majority of children with AAD are syndromic (such as Down syndrome) or genetic (such as Ehler-Danlos syndrome or Marfan syndrome). To the best of literature search, there were no reports of AAD among children with congenital hypothyroidism. This case highlights an uncommon association of AAD presenting with features of compressive myelopathy in a child with congenital hypothyroidism. Early detection and neurosurgical intervention could possibly avert this irreversible neurological damage.

INTRODUCTION

Atlantoaxial dislocation (AAD) refers to a loss of stability between the atlas and axis (C1 and C2), resulting in loss of normal articulation and movement. Stability of this articulation can be lost due to traumatic, inflammatory, idiopathic, or chromosomal disorder or congenital abnormalities.[1] Neurological sequelae such as compressive myelopathy, respiratory depression, and rarely death have been reported in untreated cases of AAD.[2] Most of the cases of AAD in children have a definite syndromic cause such as Down syndrome for their craniovertebral junction pathology.

To the best of the literature search, there are no reports associating congenital hypothyroidism with AAD. This case describes an uncommon association of AAD presenting with features of compressive myelopathy in a child with congenital hypothyroidism. Regular follow-up and screening for AAD among children with congenital hypothyroidism as in Down syndrome could possibly avert serious neurological sequelae.[3]

CASE HISTORY

A 4-year-old boy presented with complaints of difficulty in walking with progressive weakness and decrease in muscle mass of both lower limbs for 3 months. He was diagnosed with congenital hypothyroidism at the age of 3 months and was on levothyroxine (50 µg/day) since then. The current symptom of the weakness of both lower limbs was insidious in onset and progressive in nature. He could stand without support but could ambulate only with assistance. He could not convey any positive or negative sensory symptoms. There was no bladder retention, dribbling of urine, or altered bowel habit. There was no history of difficulty in vision, seizure, or altered sensorium. There was no history of fever, weight loss, trauma, and pain in the back or in the limbs.

He was a product of a nonconsanguineous marriage, born at term gestation with an uneventful perinatal period. There was no maternal history of any significant medical illness including hypothyroidism. He had a global developmental delay with the delayed attainment of motor, speech, and cognitive milestones. Before the onset of these neurological complaints, he could walk and run independently, could speak sentences of two to three words, and could comprehend most of the verbal commands.

On examination, his heart rate and blood pressure were found to be within age-matched norms. His height was corresponding to Minus 1 to Minus 2 Standard Deviation, when compared to age and gender matched World health organization (WHO) growth charts with an upper segment:lower segment ratio was 1.4:1. There was no evident dysmorphism or any neurocutaneous markers. The neck was short with restricted movement across all directions. There was no skin hyper extensibility, chest deformity, scoliosis, or joint laxity in any of the limb joints. Eye examination was normal with no evidence of ectopia lentis or blue sclera.

Higher mental functions were appropriate for age and development. Cranial nerve examination was unremarkable. On motor examination, the bulk of all muscle was decreased in both lower limbs with sparing of upper limb muscles. The tone was decreased and power was graded as 4/5 (Medical Research Council grading) across the proximal and distal joints of the lower limb. Deep tendon reflexes were exaggerated (3+) in all four limbs with extensor plantar response. Sensations of pain, touch, and temperature were preserved as far as tested.

Magnetic resonance imaging (MRI) of the brain with cervical spine screening revealed increased atlantodental interval (ADI) (5.1 mm) with mild retroflection of dens leading to compression and thinning of cervicomedullary junction and compressive myelomalacia [Figure 1]. X-ray of the cervical spine (dynamic scan) revealed increased ADI of >4.5 mm. Radiograph of the skull was normal with no evidence of Wormian bones. His last thyroid-stimulating hormone (TSH) level was 4.1 mIU/L. His serial TSH recording in the past 3 years conducted at 6 monthly intervals was in the normal range. Neurosurgical intervention was performed. There was no neurological recovery following surgical intervention possibly owing to myelomalacia changes.

Figure 1

MRI of the cervical spine showing compression at C1 and C2 level resulting from AAD

DISCUSSION

This case highlights an uncommon neurological complication arising from AAD in a child with congenital hypothyroidism. AAD is commonly associated with genetic conditions such as Down syndrome, achondroplasia, osteogenesis imperfecta, Morquio syndrome, and cleidocranial dysplasia.[3] Inflammatory conditions including juvenile rheumatoid arthritis, lupus arthritis, psoriasis, and Grisel’s syndrome are some of the acquired causes of AAD.[4] Traumatic AAD in the absence of another predisposing risk factor is extremely uncommon.[5]

Joint hypermobility can result from genetic causes such as Ehler–Danlos syndrome, Marfan syndrome, or skeletal dysplasia. Most of these cases unlike this case have joint hypermobility, skin hyperlaxity, hypotonia with radiograph showing Wormian bones. The term hypermobility refers to excessive movement across the plane whereas hyperlaxity refers to excessive movement in the abnormal plane as in AAD.[1] AAD is a common (15%–20%) comorbidity in children with Down syndrome. Predisposing factors include hypermobility and instability caused by ligamentous laxity and osseous abnormalities, resulting in an increased incidence of AAD.[6] There is no literature to support joint hypermobility among children with congenital hypothyroidism. However, calcific tendinitis of shoulder joints has been reported among adults with hypothyroidism.[7]

The clinical presentation of AAD includes neck pain, neck movement restriction, compressive myelopathy manifesting with quadriplegia, sphincter disturbances, lower cranial nerve dysfunction, and respiratory distress.[8] Other serious sequelae include respiratory failure, vertebral artery dissection, and rarely death if left untreated.[8910] Neurological manifestations of congenital AAD in children result from progressive compression of the cervicomedullary junction.[11]

Most of the pediatric patients with AAD might have some syndromic association, or traumatic or inflammatory conditions. AAD is a radiological diagnosis based on measurements of atlantoaxial joint articulation using the ADI with a normal interval of 4.5 mm in children.[12] Dynamic cervical radiographs are often used to diagnose atlantoaxial instability and dislocation but could be falsely positive owing to muscle spasms.[8] However, computed-tomography scan is a useful investigation to see the multidimensional involvement. In addition, MRI of the cervical spine provides soft-tissue involvement including spinal abnormality.

This case highlights an uncommon etiology of AAD as congenital hypothyroidism. It could be a mere association rather than attributing a causative role of hypothyroidism in AAD. However, further studies on screening for AAD among children with congenital hypothyroidism are suggested based on this anecdotal experience. Early detection and neurosurgical intervention could possibly avert this irreversible neurological damage.

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Conflicts of interest

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