Combined Central and Peripheral Demyelination (CCPD): This condition, also known as chronic inflammatory demyelinating polyneuropathy (CIDP) with central nervous system involvement, is characterized by both central and peripheral demyelination, leading to symptoms such as paresthesias, weakness, and ataxia. The combination of central and peripheral symptoms makes this a strong candidate for the single most likely diagnosis.

Multiple Sclerosis (MS): While primarily a central demyelinating disease, MS can occasionally present with peripheral nervous system involvement, leading to a combination of central and peripheral symptoms. The presence of paresthesias is common in MS.
Chronic Inflammatory Demyelinating Polyneuropathy (CIDP): CIDP is an autoimmune disorder that causes peripheral nerve demyelination, leading to symptoms like paresthesias, weakness, and gait difficulties. Some forms of CIDP may have central nervous system involvement, although this is less common.
Neuropathy with IgM Monoclonal Gammopathy: This condition involves the production of IgM antibodies that can target myelin, leading to demyelinating neuropathy. Paresthesias are a common symptom, and there can be central nervous system involvement in some cases.

Vitamin B12 Deficiency: A deficiency in vitamin B12 can cause both central and peripheral demyelination, leading to symptoms such as paresthesias, weakness, and ataxia. This condition is treatable with supplementation, making it crucial not to miss.
Lyme Disease: Neuroborreliosis, the neurological manifestation of Lyme disease, can cause central and peripheral nervous system symptoms, including demyelination and paresthesias. Early diagnosis and treatment are essential to prevent long-term sequelae.
Sarcoidosis: This autoimmune disease can affect multiple systems, including the nervous system, causing both central and peripheral demyelination. Neurosarcoidosis can present with a wide range of symptoms, including paresthesias.

Tangier Disease: A rare genetic disorder characterized by severe reduction in HDL cholesterol, leading to peripheral neuropathy and potentially central nervous system involvement.
Refsum Disease: A genetic disorder that affects the metabolism of a specific fatty acid, leading to demyelinating neuropathy and potentially central nervous system symptoms.
Metachromatic Leukodystrophy: A genetic disorder that affects the breakdown of fatty substances, leading to both central and peripheral demyelination. It is rare and typically presents in childhood, but adult-onset cases can occur.