Clinical Scenario:
A 15-year-old boy presents with a 1-year history of progressive weakness of both hands. He has difficulty with buttoning his clothes and writing. On examination, there is bilateral wasting and weakness of the small muscles of the hands, with reduced tone and absent upper-limb reflexes.
In the lower limbs, muscle tone is increased and deep tendon reflexes are brisk bilaterally, with bilateral extensor plantar responses.
Sensory examination reveals bilateral loss of pain and temperature sensation over the shoulders, upper chest and medial aspects of the arms, while vibration sense is preserved.
Which of the following is the most likely diagnosis?
A. Cervical radiculopathy
B. Syringomyelia
C. Subacute combined degeneration
D. Motor neuron disease
E. Friedreich ataxia
Correct answer & Explanation:
Explanation
Correct answer: B. Syringomyelia
The combination of lower motor neuron (LMN) signs in the upper limbs, upper motor neuron (UMN) signs in the lower limbs, and dissociated sensory loss is characteristic of a cervical syrinx.
The wasting and weakness of the small muscles of the hands with reduced tone and absent upper-limb reflexes result from involvement of the anterior horn cells at the level of the cervical syrinx.
As the syrinx extends laterally and involves the corticospinal tracts, it produces UMN signs below the level of the lesion. Therefore, increased tone, brisk lower-limb reflexes and extensor plantar responses may develop.
The sensory finding is particularly important. A central syrinx initially damages the crossing spinothalamic fibers, resulting in loss of pain and temperature sensation in a characteristic cape-like distribution over the shoulders, upper arms and upper trunk.
The dorsal columns are typically spared, so vibration and proprioception remain preserved in classic syringomyelia. This is called dissociated sensory loss.
Exam pearl
Hand wasting + absent upper-limb reflexes + brisk lower-limb reflexes + loss of pain and temperature with preserved vibration = syringomyelia.
In children and adolescents, an important underlying association is Chiari I malformation, although syringomyelia can have other causes. MRI of the brain and spinal cord is the investigation of choice.
Reference
StatPearls. Syringomyelia. NCBI Bookshelf.
MSD Manual Professional Edition. Syrinx of the Spinal Cord or Brain Stem. Updated March 2025.
