This One's for Mal: Selective Cerebral Vulnerability and the Thiamine-Dependent Metabolic Reserve Hypothesis of Dementia

Dementia presents through selective cognitive and network failure rather than simultaneous global cerebral dysfunction, and pathological burden may precede clinical expression. This paper develops a thiamine-dependent metabolic reserve hypothesis to explain one possible contributor to that transition. Thiamine pyrophosphate (TPP) supports pyruvate dehydrogenase, α-ketoglutarate dehydrogenase, transketolase, and related metabolic processes. Abnormalities involving multiple TPP-dependent enzymes and reduced cortical TPP have been reported in Alzheimer disease (AD), while experimental thiamine deficiency can produce selective metabolic dysfunction and neuronal injury. These observations do not establish causation, and postmortem data cannot resolve temporal direction. The proposed Dynamic Reserve framework defines functional reserve as the margin between effective thiamine-dependent metabolic capacity and prevailing physiological demand. The associated Selective-Vulnerability Principle predicts that neural systems may cross functional thresholds at different times according to differences in demand, connectivity, compensatory capacity, transport, and intrinsic susceptibility. The Compartment Rule further distinguishes systemic status from cerebral function: low whole-blood TPP supports systemic depletion, whereas normal or elevated whole-blood TPP does not by itself establish adequate cerebral intracellular or mitochondrial TPP availability, enzyme engagement, or metabolic flux. Under the causal-completion hypothesis, loss of thiamine-dependent metabolic capacity may become the limiting event that converts compensated pathology into clinically manifest dysfunction and, if sufficiently severe or prolonged, may contribute to structural injury. Alzheimer’s disease provides the strongest current evidentiary test case; extension to other dementias remains hypothesis-level and requires independent adjudication. Existing intervention studies are limited and route-specific. This work predicts that intramuscular thiamine will prove superior to oral and intravenous administration for the chronic metabolic state proposed here and recommends direct clinical evaluation of that route. The model is falsifiable through prospective evidence addressing cerebral metabolic function, temporal order, target engagement, reversibility, and direct route comparison.