Lambert-Eaton syndrome (autoantibodies to calcium channels in presynaptic motor nerve terminals): reduced ACh release; may be associated with malignancy

Neurasthenia: weakness/fatigue without underlying organic disorder

Drug-induced myasthenia:penicillamine may cause myasthenia gravis (MG); resolves weeks to months after discontinuing drug.

Botulism: toxin inhibits presynaptic ACh release; most common form is food-borne.

Diplopia from an intracranial mass lesion: compression of nerves to extraocular muscles or brainstem lesions affecting cranial nerve nuclei

Hyperthyroidism

Progressive external ophthalmoplegia: seen in rare mitochondrial disorders that can be detected with muscle biopsy