Vitamin B12 Deficiency: This condition is a common cause of numbness in the hands and feet due to its role in the production of myelin, the protective sheath around nerve fibers. The tongue numbness could be related to the neurological effects of B12 deficiency, which can also cause changes in sensation.

Diabetes Mellitus: High blood sugar levels can damage nerves, leading to numbness in the hands and feet, a condition known as diabetic neuropathy. Tongue numbness is less common but can occur due to the widespread nature of neuropathic damage.
Hypothyroidism: This condition can cause numbness or tingling in the hands and feet due to its effects on the nervous system. While less common, some patients might experience oral symptoms, including tongue numbness.
Multiple Sclerosis: An autoimmune disease that affects the brain and spinal cord, leading to a wide range of neurological symptoms, including numbness in various parts of the body, including the hands, feet, and potentially the tongue.

Guillain-Barré Syndrome: A rare but serious condition where the immune system attacks the nerves, leading to muscle weakness and numbness that can rapidly progress. It's crucial to identify this condition early due to its potential for severe outcomes, including respiratory failure.
Lyme Disease: Caused by a bacterial infection, Lyme disease can lead to neurological symptoms, including numbness and tingling in the hands and feet. While tongue numbness is less commonly reported, the disease's potential severity warrants its inclusion in the differential diagnosis.
Syringomyelia: A disorder that causes a cyst to form within the spinal cord, leading to numbness and weakness, typically starting in the hands. This condition can progress and affect other areas, including the feet and potentially cause oral symptoms.

Sjögren's Syndrome: An autoimmune disorder that primarily affects the glands that produce tears and saliva but can also cause neurological symptoms, including numbness.
Peripheral Artery Disease (PAD): While more commonly associated with leg pain during walking, severe PAD could potentially lead to numbness in the feet due to reduced blood flow.
Amyloidosis: A group of diseases that result from the abnormal accumulation of amyloid proteins in various tissues, which can lead to neuropathy and numbness in the hands and feet. Oral symptoms, including tongue numbness, could occur in some cases due to the systemic nature of the disease.