What Causes Muscle Weakness?

Patient Presentation
A 9-year-old male came to clinic with rhinitis and left ear pain that began 2 days before. The ear pain was intermittent and there was no fever. He had been otherwise well and had not seen a physician for 3-4 years, “Because he’s never sick,” said his father. The past medical history was non-contributory. The family history was positive for stroke and depression. There were no mental, genetic, or neurological diseases in the family. The father had an adult male first cousin who walks on his toes without any other gait problems.

The pertinent physical exam showed a healthy boy with normal growth parameters. His temperature was 100.6°F. HEENT showed clear rhinorrhea and a normal pharynx. His left ear had a small amount of fluid but was grey and had normal landmarks. During the examination the physician noted that the boy seemed somewhat floppy in the way he walked to the table and got onto it. His neurological examination was remarkable for some mild hypotonia generally, muscle strength that was against gravity and some resistence, but he easily tired. There were 4 beats of clonus in both ankles. He had normal rapid alternating movements, finger-to-nose and no pronator drift. No soft neurological signs were seen during the examination. When asked to heel-toe walk along a line on the tiles he was not able to coordinate it, nor could he duck walk. When walking normally he would toe walk. His heel cords were somewhat tight. When attempting a Gower maneuver he was able to stand without assistance but did rest one hand on a leg. When he got up from a chair he was also observed to push off the father and the chair.

The diagnosis of otalgia with serous otitis media was made. The father reported that his son was “not the most athletic or coordinated” and the boy had a lot of problems with handwriting. It took him a long time to write and it was very messy. The father denied him sitting in a “W” position or wrapping his legs around chairs for stability. The diagnosis of a possible underlying neuromuscular problem was considered because of the toe-walking, mild hypotonia and weakness.

The work-up included calcium, magnesium, phosphorus, potassium, creatinine phosphokinase, lactate dehydrogenase, aldolase and thyroid function tests which were performed and were normal. The physician talked with the family that this could be a mild form of a neuromuscular problem that the child should be evaluated for so that possible treatments and assistance could be offered. The patient was referred to a pediatric neurologist and some exercises to stretch his heel cords were demonstrated. The physician said that other help such as formal physical therapy, occupational therapy, or orthopaedics consultations might be done based on what the neurologist discovered.

Muscle tone is the slight tension that is felt in a muscle when it is voluntarily relaxed. It can be assessed by asking the patient to relax and then taking the muscles through a range of motion such as moving the wrists, forearm and upper arm. Muscle strength is the muscle’s force against active resistance. Impaired strength is called weakness or paresis. There are 5 levels of muscle strength.

  • 0 = No muscle contraction detected
  • 1 = Barely detected flicker of contraction
  • 2 = Active movement with gravity eliminated
  • 3 = Active movement against gravity
  • 4 = Active movement against gravity and some resistance
  • 5 = Active movement against full resistance. This is normal muscle strength.

Toe walking is common in toddlers who are learning to walk. It becomes less common as children age. The most common reason for toewalking is tight heel cords or an undiagnosed neurological problems such as mild spastic diplegic cerebral palsy, muscular dystrophy, or spina bifida occulta.
Stretching of heel cords can improve the problem.

Learning Point
The differential diagnosis of hypotonia with and without weakness includes:

  • Hypotonia with weakness
    • Acute
      • Botulism
      • Diphtheria
      • Hypokalemia
      • Guillian Barre syndrome
      • Mental illness
        • Hysteria
        • Malingering
      • Polyneuropathies
      • Poliomyelitis
      • Transverse myelitis
    • Chronic
      • Muscle or nerve disease
        • Muscular dystrophy – Duchenne’s, Wernig-Hoffman syndrome, myotonic dystrophy
        • Peroneal nerve atrophy
        • Spinal muscle atrophy
      • Autoimmune
        • Dermatomyositis
        • Myasthenia gravis
        • Systemic lupus erythematosis
      • Central nervous system
        • Amyotrophic lateral sclerosis
        • Cervical spinal cord injury
        • Static encephalopathy
        • Space occupying lesions
      • Metabolic
        • Glycogenoses
        • Lipoidoses
        • Mucopolysaccharidoses
        • Myoglobinuria
        • Organic acidurias
        • Parathyroidism – hypo and hyper
        • Porphyria
      • Syndromes
        • Leigh
        • Krabbe
        • Lowe
        • McCardle
        • Refsum
      • Disuse
    • Hypotonia without weakness
      • Cerebral palsy – hypotonic form
      • Benign congenital hypotonia
      • Metabolic disease
        • Celiac Disease
        • Congenital heart disease
        • Hypothyroidism
        • Hypercalcemia
        • Renal tubal acidosis
        • Rickets
      • Syndrome and Genetic diseases
        • Down syndrome
        • Ehler-Dahlos
        • Marfan
        • Prader-Willi
        • Rett

    For hypotonia in an infant, click here.

    Questions for Further Discussion
    1. What other professionals might be needed by this child?
    2. What are indications for a muscle biopsy?
    3. What are indications for a genetics evaluation?

    Related Cases

    To Learn More
    To view pediatric review articles on this topic from the past year check PubMed.

    Evidence-based medicine information on this topic can be found at SearchingPediatrics.com, the National Guideline Clearinghouse and the Cochrane Database of Systematic Reviews.

    Information prescriptions for patients can be found at MedlinePlus for these topics: Myositis and Muscular Dystrophy.

    To view current news articles on this topic check Google News.

    To view images related to this topic check Google Images.

    To view videos related to this topic check YouTube

    Sheldon SH Levy HB. Pediatric Differential Diagnosis. 2nd Edit. Second Edition. Raven Press: New York. 1985:177-183.

    Bates B. Guide to Physical Examination. Third Edit. Lippincott Company, Philadelphia, PA. 1986:390.

    Illingworth RS. Common Symptoms of Disease in Children. Blackwell Scientific Publications: Oxford. 1988:256-260.

    Huff KR. Hypotonia, in Pediatrics a Primary Care Approach, Berkowitz CD, ed. W.B. Saunders Co. Philadelphia, PA. 1996;369-373.

    ACGME Competencies Highlighted by Case

  • Patient Care
    1. When interacting with patients and their families, the health care professional communicates effectively and demonstrates caring and respectful behaviors.
    2. Essential and accurate information about the patients’ is gathered.
    3. Informed decisions about diagnostic and therapeutic interventions based on patient information and preferences, up-to-date scientific evidence, and clinical judgment is made.
    4. Patient management plans are developed and carried out.
    5. Patients and their families are counseled and educated.
    7. All medical and invasive procedures considered essential for the area of practice are competently performed.
    8. Health care services aimed at preventing health problems or maintaining health are provided.
    9. Patient-focused care is provided by working with health care professionals, including those from other disciplines.

  • Medical Knowledge
    10. An investigatory and analytic thinking approach to the clinical situation is demonstrated.
    11. Basic and clinically supportive sciences appropriate to their discipline are known and applied.

  • Interpersonal and Communication Skills
    19. The health professional works effectively with others as a member or leader of a health care team or other professional group.

  • Professionalism
    20. Respect, compassion, and integrity; a responsiveness to the needs of patients and society that supercedes self-interest; accountability to patients, society, and the profession; and a commitment to excellence and on-going professional development are demonstrated.
    21. A commitment to ethical principles pertaining to provision or withholding of clinical care, confidentiality of patient information, informed consent, and business practices are demonstrated.
    22. Sensitivity and responsiveness to patients’ culture, age, gender, and disabilities are demonstrated.


    Donna M. D’Alessandro, MD
    Professor of Pediatrics, University of Iowa Children’s Hospital