Limb Stiffness in Hyponatremia
Limb stiffness in hyponatremia occurs due to osmotic demyelination syndrome (also called central pontine myelinolysis), which results from overly rapid correction of chronic hyponatremia, causing demyelination of neurons in the brainstem and other brain regions. 1, 2
Mechanism of Limb Stiffness
Osmotic demyelination syndrome develops when chronic hyponatremia is corrected faster than 8 mmol/L in 24 hours, causing rapid osmotic shifts that damage the myelin sheaths of neurons 1, 2, 3
The syndrome typically manifests 2-7 days after rapid correction, presenting with dysarthria, dysphagia, oculomotor dysfunction, quadriparesis, and limb stiffness 2
Neurological manifestations include parkinsonism, spastic quadriparesis, pseudobulbar palsy, and in severe cases, a "locked-in" syndrome with preserved consciousness but inability to move 1, 3
The stiffness results from upper motor neuron damage in the pons and extrapontine sites, leading to spasticity and rigidity of the limbs 1, 2
High-Risk Populations
Patients with advanced liver disease, alcoholism, malnutrition, severe hyponatremia, or prior encephalopathy face the highest risk and require correction rates limited to 4-6 mmol/L per day 2
Cirrhotic patients have an estimated 0.5-1.5% risk of osmotic demyelination syndrome following liver transplantation 2
Critical Prevention Guidelines
The maximum safe correction rate is 8 mmol/L in 24 hours for average-risk patients 1, 2, 3
For high-risk patients, limit correction to 4-6 mmol/L per day, with an absolute maximum of 8 mmol/L in 24 hours 2
Monitor serum sodium every 2 hours during initial correction in severe symptomatic cases, then every 4 hours after symptom resolution 2
Management of Overcorrection
If sodium correction exceeds 8 mmol/L in 24 hours, immediately discontinue current fluids and switch to D5W (5% dextrose in water) 2
Consider administering desmopressin to slow or reverse the rapid rise in serum sodium 2
The goal is to relower sodium to bring total 24-hour correction to no more than 8 mmol/L from the starting point 2
Important Distinction
Limb stiffness from osmotic demyelination is iatrogenic (treatment-related), not a direct symptom of hyponatremia itself 1, 3
Acute symptomatic hyponatremia causes cerebral edema with symptoms like confusion, seizures, and coma—not limb stiffness 3, 4
Chronic mild hyponatremia causes gait disturbances, falls, and cognitive impairment, but not the spastic limb stiffness seen in osmotic demyelination 3