DDx for Muscle Weakness

1) Muscle:
a) Congenital myopathies and mitochondrial myopathies: Sx. bilateral, proximal to distal wasting. Dx: elevated CK and LDH, abnormal EMG, normal nerve conduction. definite diagnosis with genetic testing.
b) Polymyositis: Abnormal CK and LDH, Dx with muscle biopsy
c) Dermatomyositis: Abnormal CK and LDH, Dx made with muscle biopsy
d) CREST syndrome: Anti-centromere ab
2) NMJ
a) Myesthenia gravis: Dx with EMG. Contractile force reduced with repetition
b) Lambart-Eaton: Dx with EMG. Contractile force increased with repetition
3) PNS
a) Diabetic Neuropathy: loss of sensation first. abnormal NC labs
b) Peripheral nerve degeneration/demyelination. Abnormal NC studies. Weakness in isolated motor neauron units
c) Radiculopathy: weaknes in motor neuron unit bundles. Abnormal NC studies
4) CNS
a) Gullian-Barre: ascending progression. increased ab levels in CSF
b) MS: lesions on CNS on MRI
c) B12 deficiency: depleted B12 levels
d) Polio
e) ALS: intact sensation, both upper neuron and lower neuron signs