Guillain-Barré Syndrome: An autoimmune disorder that is the most common cause of flaccid quadriaparesis, characterized by rapid onset of muscle weakness, often following a minor infection. It affects the peripheral nervous system, leading to ascending paralysis.

Spinal Cord Injury: Trauma to the spinal cord can result in flaccid quadriaparesis, depending on the level and severity of the injury. The initial phase post-injury may present with flaccidity due to spinal shock.
Polio (Poliomyelitis): Although largely eradicated in many parts of the world, polio remains a cause of flaccid paralysis in areas where vaccination is not widespread. It is caused by the poliovirus, which affects motor neurons.
Toxic Neuropathies: Certain toxins (e.g., heavy metals like lead or arsenic, and some drugs) can cause peripheral neuropathy leading to flaccid weakness.

Botulism: A potentially life-threatening illness caused by a toxin produced by Clostridium botulinum. It leads to descending flaccid paralysis, starting with cranial nerves and progressing downward.
Tick Paralysis: A rare condition caused by the neurotoxin in the saliva of certain ticks. It can lead to ascending flaccid paralysis similar to Guillain-Barré Syndrome.
Diphtheria: A bacterial infection that can cause a toxin-mediated neuropathy leading to flaccid paralysis, among other symptoms.

Porphyria: A group of disorders that can lead to acute intermittent porphyria, which may present with neurological symptoms including flaccid quadriaparesis.
Critical Illness Neuropathy: Seen in patients with prolonged critical illness, it can cause flaccid weakness due to muscle and nerve damage.
Inherited Neuropathies: Certain genetic conditions, such as Charcot-Marie-Tooth disease, can lead to progressive flaccid weakness, though they typically have a slower onset than acute quadriaparesis.