- Insidious onset (HP:0003587): Gradual, very slow onset of disease manifestations. Evidence: IEA. (OMIM:602440)
- Interosseus muscle atrophy (HP:0007181): Atrophy of the interosseus muscles (including the palmar interossei that lie on the anterior aspect of the metacarpals, the dorsal interosseus muscles of the hand, which lie between the intercarpals, the plantar interosseus muscles, which lie underneath the metatarsal bones, and the dorsal interossei, which are located between the metatarsal bones. Evidence: TAS. (OMIM:602440)
- EMG: neuropathic changes (HP:0003445): The presence of characteristic findings of denervation on electromyography (fibrillations, positive sharp waves, and giant motor unit potentials). Evidence: IEA. (OMIM:602440)
- Upper limb muscle weakness (HP:0003484): Weakness of the muscles of the arms. Evidence: TAS. (OMIM:602440)
- Cold paresis (HP:0031372): Increased muscle weakness upon exposure to cold temperatures. Evidence: IEA. (OMIM:602440)
- Fasciculations (HP:0002380): Fasciculations are observed as small, local, involuntary muscle contractions (twitching) visible under the skin. Fasciculations result from increased irritability of an axon (which in turn is often a manifestation of disease of a motor neuron). This leads to sporadic discharges of all the muscle fibers controlled by the axon in isolation from other motor units. Evidence: IEA. (OMIM:602440)
- Cervical spinal cord atrophy (HP:0010873): Atrophy of the cervical segment of the spinal cord. Evidence: IEA. (OMIM:602440)
- Sporadic (HP:0003745): Cases of the disease in question occur without a previous family history, i.e., as isolated cases without being transmitted from a parent and without other siblings being affected. Evidence: IEA. (OMIM:602440)
These phenotypes are associated with the disease monomelic amyotrophy (OMIM:602440).