What are the causes of hypertonicity of the legs?

Causes of Hypertonicity of the Legs

Hypertonicity of the legs is primarily caused by upper motor neuron lesions resulting in spasticity, dystonia, or rigidity, with spasticity being the most common manifestation following stroke, traumatic brain injury, or spinal cord injury. 1, 2

Neurological Causes

• Upper Motor Neuron Syndrome: Damage to descending motor pathways leads to reduced inhibitory activity within spinal cord circuits and adaptive changes within motoneurons, causing velocity-dependent increase in muscle tone 3, 4
• Stroke: Common cause of hypertonicity, particularly affecting flexor muscles distally and adductors, flexors, and internal rotators at proximal joints 1
• Traumatic Brain Injury: Can lead to spasticity as part of the upper motor neuron syndrome 2
• Spinal Cord Injury: Results in hypertonicity below the level of injury 4
• Multiple Sclerosis: Progressive demyelination can cause hypertonicity 2
• Cerebral Palsy: Leading cause of hypertonicity in pediatric populations 2
• Neurodegenerative Diseases: Conditions like neurodegeneration with brain iron accumulation (NBIA) can present with progressive gait disturbances, dystonia, and spasticity 5

Medication-Related Causes

• Neuroleptic Malignant Syndrome (NMS): A potentially lethal syndrome characterized by mental status changes, fever, hypertonicity/rigidity, and autonomic dysfunction, caused by dopamine receptor blockade 5
• Antipsychotic Medications: Can cause acute extrapyramidal syndromes including acute dystonia and Parkinsonian syndrome with rigidity 5
• Medication Withdrawal: Sudden discontinuation of baclofen or other antispasticity medications can worsen hypertonicity 3

Metabolic Causes

• Hypernatremia: Relative excess of body sodium over body water can lead to hypertonicity affecting muscles 6
• Hyperglycemia: Severe hyperglycemia can cause hypertonicity through osmotic effects 6

Assessment of Leg Hypertonicity

• Modified Ashworth Scale: Measures resistance to passive movement; most commonly used despite questions about validity and interrater reliability 5, 1
• Modified Tardieu Scale: Assesses spasticity at different velocities of movement 1
• Spasm Frequency Scale: Quantifies the frequency of muscle spasms 1
• Fugl-Meyer Assessment: Evaluates motor recovery after stroke including hypertonicity 1
• Physical Examination: Should include assessment of resistance to movement at rest and observation of patterns of tightness during functional activities 1, 4

Management Approaches

Non-pharmacological Interventions

• Physical Therapy: First-line treatment including stretching, strengthening of antagonist muscles, and range of motion exercises 3, 4
• Positioning: Proper positioning and seating can help manage hypertonicity 4
• Splinting and Casting: Maintain muscle stretch and optimal positioning 4

Pharmacological Interventions

• Oral Medications:

  • Baclofen: GABAB agonist, first-line for generalized spasticity (30-80 mg/day divided into 3-4 doses) 7
  • Tizanidine: Alpha-2 adrenergic agonist for spasticity, with common side effects including dry mouth (49%), somnolence (48%), and asthenia (41%) 8
  • Dantrolene: Acts directly on muscle to reduce contraction 7

• Focal Interventions:

  • Botulinum Toxin: First-line for focal spasticity, shown to decrease tone and improve function 7, 1
  • Phenol Injections: Alternative for focal spasticity 1, 3

• Advanced Interventions:

  • Intrathecal Baclofen: For severe spasticity unresponsive to oral medications, with >80% of patients showing improvement in muscle tone 7
  • Surgical Procedures: Include selective dorsal rhizotomy or dorsal root entry zone lesion for severe cases 7, 3

Special Considerations

• Nociceptive Stimuli: Urinary tract infections, skin breakdown, and other painful conditions can worsen hypertonicity 4
• Secondary Changes: Prolonged hypertonicity can lead to contractures and weakness, requiring comprehensive rehabilitation 1
• Comorbid Conditions: Peripheral neuropathy with loss of protective sensation may limit weight-bearing exercise and require special attention 5

Treatment Algorithm

1. Identify and treat underlying cause (stroke, TBI, etc.) 4
2. Address nociceptive triggers (infections, pressure sores) 4
3. First-line approaches: Physical therapy, positioning, stretching, splinting 7, 4
4. For generalized hypertonicity: Oral medications (baclofen, tizanidine, dantrolene) 7, 3
5. For focal hypertonicity: Botulinum toxin or phenol injections 7, 1
6. For severe, refractory cases: Intrathecal baclofen or surgical interventions 7, 3