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NEUROMUSCULAR EVALUATION PROTOCOLS

HISTORY & PHYSICAL EXAMINATION: Clinical patterns*

NEUROMUSCULAR LABORATORY TESTING
  Especially for treatable diagnoses
  After history & examination

Antibodies   Requisition   Instructions Biopsy   Muscle   Nerve   Requisition Myasthenia gravis Myopathy   Antibodies   Creatine Kinase (CK):     Very High     Unexpectedly High   Muscle biopsy Neuropathy   Antibodies   Biopsy   Motor   Sensory, or sensory-motor

Duchenne

Motor neuropathy-Motor neuron syndromes

• Multifocal motor neuropathy (MMN)
  • Anti-GM1 antibodies: Indications
  • Only use laboratories that find IgM anti-GM1 antibodies in
    • > 40% of patients with MMN
    • < 2% of patients with ALS
• M-protein
  • Immunofixation methodology should be used.
  • Check in serum & urine.
  • Serum protein electrophoresis and immunoelectrophoresis are not sensitive enough to detect many M-proteins
  • Also measure quantitative immunoglobulins
• Anatomical evaluation of spine & posterior fossa
• Electrodiagnostic testing
  • Rule out: Focal nerve lesion(s); Conduction block
  • Neuropathy vs. Myopathy
• Genetic testing: Usually with symmetric weakness
  • Hexosaminidase A (multisystem disorder)
  • Spinal muscular atrophy (SMN deletion)
  • Bulbo-spinal muscular atrophy (Androgen receptor triplet repeat)
• Other less common etiologies: Often acute or subacute weakness
  • Toxic: Serum lead ± heavy metals
  • Porphyria
    • δ-amino levulinic acid & porphobilinogen (24-hour urine), or
    • Uroporphobilinogen-1-synthetase
• Muscle biopsy: Rule out inflammatory or distal myopathy
• Nerve biopsy: Rarely, indicated

Sensory & sensory-motor neuropathies

• Diabetes
  • Hemoglobin A1C, or
  • 2 hour p.c. blood sugar
• Vitamin E
• Vitamin B₁₂
  • If levels are low then test urine for
    • Homocysteine & methylmalonic acid
    • High values suggest that a low B₁₂ level is biologically significant
• M-protein
  • Immunofixation methodology should be used.
  • Check in serum & urine.
  • Serum protein electrophoresis and immunoelectrophoresis are not sensitive enough to detect all M-proteins
  • Also measure quantitative immunoglobulins
• Serum antibodies
  • MAG: Only use laboratory that
    • Screens with pure MAG antigen
    • Confirms positive results with Western blot
  • Sulfatide
    • Laboratory methods should be > 85% specific for sensory ± motor neuropathy
  • GALOP antigen
  • Hu
    • Mainly indicated in sensory neuronopathies with proximal sensory loss
• Cryoglobulins: Keep serum warm
• Hereditary neuropathies
  • HMSN IA: Test for PMP-22 duplication in demyelinating neuropathies without conduction block.
  • HNPP: Test for PMP-22 deletion with multiple lesions at sites of entrapment other than the carpal tunnel.
• Take history for toxin exposure
• Electrodiagnostic testing to define
  • Demyelinating vs. Axonal
  • Distinctive features of demyelination
    • Conduction block & Non-uniform slowing of NCV: Suggest acquired demyelination
    • Selectively prolonged distal latencies: Suggest IgM M-protein related neuropathy
  • Asymmetry: Suggests vasculopathy or demyelination; Nerve biopsy often useful
  • Focal nerve lesions
  • Always test upper & lower extremities to document diffuse vs. focal neuropathy
• Nerve biopsy
  • Limited number of indications
  • Biopsy underlying muscle at same time for increased diagnostic yield
• Other
  • Collagen vascular screen: ANA
  • Lipid screen
  • If paraneoplastic is considered: Chest & abdominal CT; Stool guaiac; Gynecological examination

Myasthenia Gravis

• Diagnostic tests
• Striational antibodies
• Systemic disorders: Especially thyroid
• Thymus evaluation
• Electrodiagnostic evaluation
• Assessment of vital functions
  • Respiratory: Vital capacity & NIF
  • Swallowing

Myopathy

• Identifing a disorder as myopathy
  • EMG
    • Brief, Small amplitude, Polyphasic potentials: Suggest a myopathy
    • Additional irritability (e.g. fibrillations): Suggests a possible inflammatory disorder
  • Creatine Kinase (CK)
    • Different differential when high or very high
    • CK is also often high in motor neuron disorders
• Identifying a specific etiology for a myopathy
  • Muscle biopsy
  • Inflammatory & immune myopathies
    • Collagen vascular screen
    • Antibodies ¹
    • Test for serum M-protein: Immunofixation
    • Immune stains of muscle
  • Hereditary myopathies: Analysis of muscle for
    • Dystrophy-related proteins
    • Mitochondrial disorders
    • Glycogen storage syndromes