Muscle Weakness – Proximal

Proximal weakness is usually due to dysfunction of the lower motor unit; that is, anterior horn cells in the spinal cord, neuromuscular junction (NMJ), or the muscle itself. The neurologic examination, EMG, and nerve conduction studies, and finally the muscle enzymes and biopsy, guide the diagnosis.

Differential Diagnosis

• Duchenne and Becker muscular dystrophy
• Spinal muscular atrophy
• Spinal cord disorders
  –Trauma
  –Myelitis
  –Neoplasm
  –AVM
  –Hemorrhage
  –Tansverse myelitis
• Limb-girdle myasthenia
• Dermatomyositis
• Congenital myopathies
  –Central core disease
  –Myotubular
  –Nemaline (rod)
  –Congenital fiber-type disproportion
• Facioscapulohumeral syndrome
• Limb-girdle muscular dystrophies
• Glycogen storage myopathies
• Endocrine myopathies
  –Hypo- and hyperthyroidism
  –Hyperparathyroidism
  –Adrenalism
• Polymyositis
• GM2 gangliosidosis
• Pompe disease
  –Glycogen storage disease type II
  –Acid maltase deficiency
• McArdle disease
• Carnitine deficiency
• Fatty acid oxidation defects
• Mitochondrial disorders
• Steroid-induced myopathy
• Slow channel syndrome
• Toxins
  –Organophosphates
  –Aminoglycosides
  –Tetrodotoxin (pufferfish)
• Conversion reaction
• Myasthenia gravis

Workup and Diagnosis

• History: Age upon reaching developmental milestones, abnormal gait, toe walking, easy fatigability, muscle cramps, facial weakness, cardiac, respiratory, GI problems, dark urine
• Physical exam: Muscle mass, texture and tenderness, scoliosis, cardiac exam, skin rashes, joint contractures
• Neurologic exam
  –Muscle strength and tone
  –Gowers sign
  –Mental status, eye movements
  –Facial movements, tongue fasciculations
  –Muscle stretch reflexes and sensory responses
  –Stance and gait
  –Spinal cord disorders, examine dermatomal sensory loss, anal wink, cremasteric reflex
• Labs: Muscle enzymes (CPK, aldolase); electrolytes, TSH, lactate, pyruvate, carnitine; ANA, RF, genetic testing for muscular dystrophy and spinal muscular atrophy; hexosaminidase, acetylcholine receptor antibodies, myoglobin in urine (muscle breakdown)
• EMG/nerve conduction studies
  –Differentiates dysfunction of the anterior horn cell, muscle, or neuromuscular junction
• Muscle biopsy for metabolic, inflammatory, and congenital myopathies; distinguishes myopathy from anterior horn cell disease
• MRI of the spine for spinal cord disorder
• Tensilon test for myasthenia

Treatment

• Combination of physical therapy, bracing, and orthopedic surgical interventions can help patients maintain functional motor skills
• Duchenne muscular dystrophy
  –Oral prednisone to increase and sustain muscle strength
• Endocrine myopathies
  –Treating the underlying endocrine disease corrects the myopathy and weakness
• Dermatomyositis
  –Oral prednisone
  –If resistant to oral steroids, immunosuppression with high-dose intravenous steroids, methotrexate, cyclophosphamide or intravenous immunoglobulins
• Transverse myelitis
  –Treat with high-dose intravenous steroids
• Myasthenia gravis
  –Acetylcholinesterase inhibitors (pyridostigmine), immunosuppression, and thymectomy

Book Source Details

• Book Title: In A Page: Pediatric Signs and Symptoms
• Author(s): Jonathan E. Teitelbaum, Kathleen O. Deantonis, Scott Kahan
• Year of Publication: 2007
• Copyright Details: In A Page: Pediatric Signs and Symptoms, Copyright © 2007 Lippincott Williams & Wilkins.

Other Book Chapters Related to Leg weakness

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Copyright Details: In A Page: Pediatric Signs and Symptoms, Copyright © 2008 Williams & Wilkins.

More About Causes of Leg weakness

• Back to symptom: Leg weakness: Introduction (review 147 causes)
• Next Book Extract About Leg weakness: LEG PAIN (Differential Diagnosis in Primary Care)
• All Book Extracts: All Online Book Extracts for Leg weakness

More About This Book: Title: In A Page: Pediatric Signs and Symptoms Authors: Jonathan E. Teitelbaum, Kathleen O. Deantonis, Scott Kahan Publisher: Lippincott Williams & Wilkins Copyright: 2007 ISBN: 1-4051-0427-9

 » Next page: LEG PAIN (Differential Diagnosis in Primary Care)

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