What is the approach to evaluating and managing abnormal muscle tone, including hypotonia (low muscle tone) and hypertonia (high muscle tone)?

Neuromotor Examination: Evaluating Muscle Tone

Assess muscle tone systematically by first determining whether tone is increased (hypertonia) or decreased (hypotonia), then localize the lesion based on associated reflexes and clinical features to guide appropriate diagnostic workup and management. 1

Initial Assessment Approach

Optimal Examination Conditions

• Examine children when well-rested and comfortable, though important diagnostic information can still be obtained by observing quality and quantity of movement in uncooperative toddlers and preschoolers 1
• Ensure patient relaxation during passive movement testing, as voluntary muscle activity can confound tone assessment 2

Age-Specific Tone Assessment Techniques

Infants:

• Assess postural tone via ventral suspension in younger infants 1
• Evaluate truncal positioning when sitting and standing in older infants 1
• Document the scarf sign in infants to monitor extremity tone 1
• Measure popliteal angles after the first year of life 1

Older Children:

• Observe functional activities: tripod sitting, walking, running, climbing, hopping, and skipping 1
• Look for Gower maneuver (inability to rise from floor without pushing up with arms), which indicates muscle weakness 1
• Assess muscle bulk, texture, joint flexibility, and presence of atrophy 1

Distinguishing Hypertonia Types

Spasticity (Upper Motor Neuron)

• Velocity-dependent resistance that increases with rapid passive movement 3
• Characteristic "catch" when threshold velocity or amplitude is reached 3
• Asymmetrically affects antagonistic muscle groups 3
• Associated findings: Increased deep tendon reflexes, abnormal plantar reflex (Babinski sign) 1
• Indicates corticoreticulospinal (pyramidal) tract damage 3

Rigidity (Extrapyramidal)

• Velocity-independent resistance constant throughout range of motion 3
• "Lead pipe" quality present in both flexors and extensors equally 3
• May have interrupted "cogwheel" quality when tremor coexists 3
• Indicates basal ganglia, mesencephalon, or spinal cord dysfunction 3

Evaluating Hypotonia

Clinical Localization

Lower Motor Neuron/Muscle Disorders:

• Diminished or absent deep tendon reflexes 1
• Associated weakness and decreased muscle bulk 1
• May have tongue fasciculations 1

Central Nervous System Disorders:

• Persistence of primitive reflexes 1
• Asymmetry or absence of protective reflexes 1
• May have associated cognitive delays 1

Key Diagnostic Maneuvers

• Observe quality of shoulder shrug 1
• Assess grasp quality and intensity during play 1
• Test for sensory deficits (touch and pain sensation) 1
• Evaluate for dyspraxia in older children through age-appropriate gross and fine motor skills 1

Initial Laboratory Workup for Hypotonia with Weakness

Mandatory first-line tests:

• Creatine phosphokinase (CK): Significantly elevated (usually >1000 U/L) in Duchenne muscular dystrophy 1
• Thyroid-stimulating hormone (TSH): Rule out hypothyroidism 1

These tests can be performed within the primary care setting before subspecialty referral 1

Critical Pitfalls to Avoid

• Do not mistake voluntary muscle activity for true tone abnormalities during passive movement—the majority of control subjects show voluntary EMG activity that can be misinterpreted as increased tone 2
• Recognize that "hypotonia" without reflex changes may actually represent weakness preventing voluntary activity rather than true tone reduction 2
• Do not overlook associated findings: Drooling or poor weight gain suggest facial/oral motor weakness; ptosis warrants further cranial nerve evaluation 1
• Remember that unsteady gait or tremor can indicate muscle weakness rather than primary cerebellar dysfunction 1

Specialized Assessments

Proprioception Testing

• Begin distally and move proximally if abnormalities detected 4
• Avoid tactile cues (don't touch nail bed or finger/toe pad) 4
• Use finger-to-nose and heel-to-shin tests for coordination assessment 4
• Evaluate postural stability in three positions: standing flat on both feet, single leg stance, and standing with eyes closed 4

Additional Neurological Examination Components

• Cranial nerves: Eye movements, visual confrontation, pupillary reactivity, red reflexes, facial expression, oromotor movement 1
• Growth parameters: Head circumference, weight, length/height plotted on appropriate growth curves to identify microcephaly, macrocephaly, or growth impairments 1

When to Refer for Subspecialty Evaluation

Immediate referral indications:

• Elevated CK concentration suggesting muscular dystrophy 1
• Focal neurologic findings, severe tone abnormalities, or abnormal deep tendon reflexes requiring brain MRI 1
• Suspected neuromuscular disorders requiring electrodiagnostic or genetic testing 1
• Bowel/bladder dysfunction with lower limb upper motor neuron signs (consider lumbar spine MRI for tethered cord) 1