Evaluation and investigations Of Neuromuscular Disorders

Neuromuscular disease

• Disorders of motor unit and excludes influences on muscular function from brain such as spasticity• Motor unit: 1) Motor neuron in brains vs anterior horn cell 2) axons = peripheral

nerve 3) neuromuscular junction 4) muscle fibers innervated by single neuron

• Size varies among different muscles and precision of muscular function required

• Suprasegemental or upper motor neuron control -> muscle tone, precision of movement, reciprocal inhibition of antagonistic muscles during movement, also inhbits monosynaptic stretch reflex

• Disease is common in children – genetics, Congenital vs acquired, acute vschronic, progressive vs static• Precise diagnosis is important because of specific therapy is available for many

diseases, requires lab confirmation because clinical manifestation overlap

Exmaples of genetics

• Chromosomal foci has been determined• Duchenne muscular dystrophy deletion of nucleotide sequence

defective protein, dystrophin

• Myotonic muscular dystrophy expansion or repetition rather than deletion

• Autosomal dominant vs recessive in different pedigrees,

• Mitochondrial myopathies specific mtDNA deletions and tRNA point mutations

Clinical Manfiestation

• Head lag when infant is pulled to a sittiing position from supine position• Sign of weakness not low tone• Hypotonia is associated with normal strength or with weakness

• Myopathies – generally, proximal distribution of weakness and muscle wasting, exception myotonic muscular dystrophy

• Nueropathy – genrally distal in distribution, exception juvenile spinal muscular dystrophy

• Involvmed of face, tongue palate extraocular muscles, distinguishes

• Tendon stretch reflexes• Lost in neuropathies and in motor neuron disease

• Fasiculation – sign of weakness, e.g., tongue, sign of denervation

• Sensory abnormality – neuropathy

• Fatiguable weakness –Neuromuscular junction disorders

• Myotonia, for specific neuropathies

Cont. Clinical Manifestations

• Myalgia – acute disease of myopathic or neurogenic origin• Acute dermatomyosits, Guillain Barre syndrome

• NOT muscular dystrophy or spinal muscular atrophy

• Can be in ischemic myopathy

• Generally denotes acuity rather than nature or process, so chronic diseases are not painful

• Contractures of muscles• In both myopathic and neurogenic diseases

• Undescended testes can be due to congenital causes like spinal muscular atrophy, myotonic muscular dystrophy and others – weakened gubernaculum that pulls the testes downward during foetal development

Labs

• Serum enzymes• Creatine Kinase CK – MM Skeletal Muscle, MB cardiac muscle, BB brain only!• Not a universal screening test , elevated in certain diseases like Duchenne

• Molecular Genetics markers• DNA markers according to clinical manifestation for a particular disease we can provide definitive diagnosis

• Nerve Conduction Velocity• Decreased conduction in neuropathies, localizing nerve injury

• Electromyography (EMG)

• Imaging of muscles

• Muscle biopsy

• Nerve biopsy• Sural nerve sampling, electron microscopy for demylination axonal swelling and others

• ECG – involvement of heart in muscular dystrophies and metabolic myopathy