Metabolic Encephalopathy: This is the most common cause of delta slowing on EEG, often resulting from conditions such as hepatic encephalopathy, sepsis, or severe metabolic disturbances. The brain's electrical activity slows down in response to the metabolic derangement.

Cerebral Ischemia/Infarction: Focal or diffuse ischemia can lead to delta slowing, depending on the area and extent of the brain affected. This is a common finding in patients with stroke or transient ischemic attacks.
Traumatic Brain Injury: Significant head trauma can cause diffuse or focal brain injury, leading to delta slowing on EEG due to the disruption of normal brain electrical activity.
Infections (Meningitis, Encephalitis): Central nervous system infections can cause inflammation and disrupt normal brain function, resulting in delta slowing on EEG.
Brain Tumors: Both primary and metastatic brain tumors can cause focal or diffuse delta slowing, depending on their location and size.

Status Epilepticus: Non-convulsive status epilepticus can present with delta slowing on EEG and is a medical emergency requiring prompt treatment.
Creutzfeldt-Jakob Disease: This rare, degenerative neurological disorder can cause rapid progression of dementia and characteristic EEG changes, including delta slowing.
Subarachnoid Hemorrhage: A sudden onset of delta slowing could indicate a subarachnoid hemorrhage, which is a life-threatening condition.

Krabbe Disease: A rare genetic disorder that affects the nervous system, leading to demyelination and potentially causing delta slowing on EEG.
Subacute Sclerosing Panencephalitis (SSPE): A rare chronic, progressive encephalitis that affects primarily children and young adults, caused by a persistent infection with the measles virus.
Hashimoto's Encephalopathy: A rare condition associated with Hashimoto's thyroiditis, characterized by encephalopathy and potentially causing delta slowing on EEG.