Muscle Weakness in Children

Aka: Muscle Weakness in Children, Motor Delay in Children, Pediatric Neuromuscular Disorder, Congenital Neuromuscular Disorder, Gross Motor Delay, Motor Developmental Delay

1. See Also
   1. Developmental Milestone
   2. Developmental Coordination Disorder (Clumsiness in Children)
   3. Muscular Dystrophy
2. Epidemiology
   1. Neuromuscular disorders are rare compared to other Developmental Disorders
      1. Neuromuscular disorders occur in early childhood in only 1 in 1000
      2. Contrast with Learning Disorders (1 in 15), Autism (1 in 88), Cerebral Palsy (1 in 303)
3. Precautions
   1. Early diagnosis is preferred
      1. Improved outcomes
      2. Improved access to services and reduction in caregiver stress
      3. Prompts genetic counseling
4. Screening
   1. See Developmental Milestone
   2. See Developmental Evaluation
   3. Using standardized tests is critical to avoid missing cases
   4. Bright Futures Forms
      1. http://brightfutures.aap.org/tool_and_resource_kit.html
   5. CDC Muscular Dystrophy
      1. http://www.cdc.gov/ncbddd/musculardystrophy/
5. History
   1. Birth history
      1. Perinatal Trauma
      2. Newborn disorders or signs
   2. Family History
      1. Weakness
      2. Developmental Delay
6. Exam
   1. See Developmental Evaluation
   2. See Gross Motor Milestone
   3. See Developmental Red Flags
   4. Assess muscle tone (increased of decreased)
      1. Scarf sign
      2. Popliteal angle measurement
   5. Infants age 4-6 months
      1. Assess for head lag with Pull-to-sit
      2. Initiate early intervention if not meeting milestones
         1. Head lag persists at 4 months or older
      3. Reassess at one month after intervention, and if not meeting Gross Motor Milestones
         1. Obtain Creatinine phosphokinase (CPK)
         2. Refer to pediatric neurology
   6. Infants age 6-9 months
      1. Assess for ability to achieve and maintain sitting position
      2. Obtain Creatinine phosphokinase (CPK) and initiate early intervention if not meeting milestones
         1. Not sitting independently by 7 months
         2. Not getting into a sitting position by 9 months
      3. Reassess at one month after intervention, and if not meeting Gross Motor Milestones
         1. Refer to pediatric neurology
   7. Children >12 months
      1. Assess gait and rise to standing
      2. Initiate early intervention or physical therapy if not meeting milestones
         1. Not walking by age 15 months
         2. Not standing from supine without support by 18 months
      3. Reassess at 18 months of age and if not meeting Gross Motor Milestones (or regression)
         1. Obtain Creatinine phosphokinase (CPK)
         2. Refer to pediatric neurology
      4. Other assessments or concerns at 18-24 months of age (and later) to prompt CPK and referral
         1. Walking or Running difficulties
         2. Frequent falling
         3. Difficulty standing from supine
            1. Unable to stand when pulled upward
            2. Hands braced on knee for support when standing (Gowers Maneuver)
7. Symptoms
   1. Muscle cramps
8. Signs: General
   1. Gross Motor Delay
      1. Delayed crawling or walking
      2. Decreased Muscle Strength
      3. Decreased neck strength and ability to hold head upright (head lag)
      4. Decreased muscle tone (floppiness)
      5. Frequent falls
   2. Other findings variably present
      1. Fine motor delay
      2. Cognitive delay
      3. Incoordination (see Clumsiness in Children)
9. Signs: Distinguishing central from peripheral cause
   1. Central Nervous System cause (e.g. Cerebral Palsy)
      1. Typically fixed deficits, with signs in neonatal period
      2. Increased Deep Tendon Reflexes and Clonus
      3. Spastic gait
      4. Variable muscle tone
      5. Toe walking (as with peripheral causes)
   2. Peripheral Nervous System or neuromuscular cause (anterior horn of spinal cord, nerve, muscle)
      1. Typically progressive worsening (often with regression from milestones)
      2. Altered chest appearance may be present (bell-shaped)
      3. Weak, blunted facial expressions
      4. High arched Palate
      5. Tongue fasciculations (esp. spinal muscular atrophy)
      6. Decreased muscle tone
      7. Decreased or absent Deep Tendon Reflexes
      8. Hyperlordotic, Waddling Gait
      9. Toe walking (as with central causes)
10. Differential Diagnosis
    1. Central cause (e.g. Cerebral Palsy)
    2. Neuromuscular disorder (e.g. Muscular Dystrophy)
    3. Hypothyroidism
    4. Congenital Heart Disease
    5. Nutritional deficiency
11. Labs: Indicated in low to normal muscle tone
    1. Creatinine Phospokinase (see CPK below)
    2. Thyroid Stimulating Hormone
    3. Liver Function Tests
       1. Serum Aspartate Aminotransferase increased (from muscle breakdown)
       2. Serum Alanine Aminotransferasencreased (from muscle breakdown)
12. Labs: Serum Creatinine Phosphokinase (CPK)
    1. Normal CPK (24 to 180 U/L)
       1. Primary Central Nervous System Disorder
       2. Normal CPK does not exclude Muscular Dystrophy
    2. Mildly increased CPK (180 to 3000 U/L)
       1. Neuromuscular Causes
          1. Spinal muscular atrophy
          2. Neuropathy
          3. Congenital Myopathy
       2. Other causes
          1. See Serum Creatinine Phosphokinase (CPK)
          2. Recent Immunizations
          3. Muscle Trauma
          4. Viral infection
       3. Plan if in this range
          1. Repeat in 2-3 weeks
          2. Refer to pediatric neurology if still increased (esp. more than three times normal)
    3. Grossly increased CPK (3000 to 50,000 U/L)
       1. Causes
          1. Duchenne Muscular Dystrophy
          2. Becker Muscular Dystrophy
       2. Plan if in this range
          1. Repeat in 1 week
             1. Refer to pediatric neurology if still in same range
             2. Repeat in 2-3 weeks if <3000 U/L on recheck to exclude muscle Trauma cause
    4. Severely increased CPK (>50,000 U/L)
       1. Admit for Acute Rhabdomyolysis
    5. References
       1. National Task Force for the early identification of childhood neuromuscular disorders
          1. http://www.childmuscleweakness.org/index.php/clinical-evaluation
13. Imaging
    1. Not typically indicated in isolated weakness
    2. Indications for MRI brain imaging: Suspected central nervous system cause
       1. Increased muscle tone
       2. Suspected Cerebral Palsy
       3. Microencephaly
       4. Macroencephaly
       5. Neurocognitive delay or regression
14. Evaluation: Gross Motor Delay
    1. Acutely ill patients (e.g. muscle pain, Dark Urine, respiratory distress or CPK>50,000)
       1. Hospitalization
    2. Central cause suspected (e.g. Cerebral Palsy)
       1. Refer to pediatric neurology
       2. Refer to early intervention
       3. Consider imaging (consider discussing with pediatric neurology)
    3. Peripheral Cause evaluation
       1. See Developmental Evaluation
       2. Perform history as above
       3. Perform exam as above to direct initial approach
          1. Refer to early intervention if indicated
          2. Refer to pediatric neurology if indicated
       4. Obtain CPK if indicated
          1. Interpret and manage as described above
15. Resources
    1. Neuromuscular Disorder videos (ChildMuscleWeakness.org)
       1. http://www.childmuscleweakness.org/index.php/videos
    2. National Task Force for the early identification of childhood neuromuscular disorders
       1. http://www.childmuscleweakness.org/index.php/clinical-evaluation
16. References
    1. Lurio (2015) Am Fam Physician 91(1): 38-44 [PubMed]