Amyotrophic Lateral Sclerosis (ALS): This condition is characterized by progressive muscle weakness and atrophy, which can start in various parts of the body, including the back, and is often accompanied by fasciculations (muscle twitching) that could be perceived as shaking. The combination of back weakness and upper extremity symptoms aligns with the potential presentation of ALS.

Multiple Sclerosis (MS): MS can cause a wide range of neurological symptoms, including weakness, tremors, and spasms, due to demyelination in the central nervous system. The symptoms can be quite varied and might include back weakness and shaking in the upper extremities.
Parkinson's Disease: While primarily known for causing resting tremors, rigidity, bradykinesia, and postural instability, Parkinson's disease can also lead to generalized weakness and could potentially cause symptoms that might be described as shaking in the upper extremities, especially if tremors are prominent.
Spinal Muscular Atrophy (SMA): SMA is a genetic disorder characterized by weakness and wasting in muscles used for movement (skeletal muscles), which could include those in the back and upper limbs, potentially leading to a presentation that includes shaking due to muscle fasciculations.

Spinal Cord Compression: This is a medical emergency that requires immediate attention. Compression of the spinal cord can cause a range of symptoms including sudden onset of back pain, weakness, and sensory changes in the limbs. The "shaking" could be due to spasticity or muscle spasms resulting from the compression.
Guillain-Barré Syndrome: An autoimmune disorder where the body's immune system mistakenly attacks part of its peripheral nervous system, leading to muscle weakness, and sometimes paralysis, which can ascend and include the upper limbs. Prompt recognition is crucial as it can lead to respiratory failure.
Botulism: A rare but potentially life-threatening illness caused by a toxin that affects the nervous system, leading to muscle weakness, paralysis, and respiratory issues. Early symptoms can include weakness and might be perceived as shaking in the limbs.

Wilson's Disease: A genetic disorder that leads to copper accumulation in the body, particularly in the liver, brain, and other organs. Neurological symptoms can include tremors, difficulty walking, and involuntary movements, which might be described as shaking.
Creutzfeldt-Jakob Disease: A rare, degenerative, fatal brain disorder that can cause a variety of neurological symptoms, including muscle weakness, tremors, and myoclonus (sudden, involuntary jerking of a muscle or group of muscles), which could be perceived as shaking.
Rabies: In its later stages, rabies can cause a range of neurological symptoms including weakness, paralysis, and spasms, but it's extremely rare and usually associated with a history of an animal bite.