Demonstrated, Inferred, and Disputed

The previous article established what two regulators concluded: that certain anti-malarial drugs can cause neuropsychiatric effects capable of outlasting the period of use, some possibly permanent, in people who cannot be identified in advance.

Regulators reached those conclusions without explaining them. They found that the effects occur. They did not establish what is happening in the nervous system to produce them.

That question — the mechanism — is where the evidence changes character. A reader who understands the difference here will be able to judge everything that follows.

What was demonstrated Demonstrated

The strongest mechanistic evidence comes from animal research. In 2006, a study published in Antimicrobial Agents and Chemotherapy examined dose-related neurological effects of mefloquine in a rat model. The researchers found degeneration in specific brainstem structures — the nucleus gracilis, the nucleus cuneatus, and the solitary tract.

The authors described the degeneration as permanent in nature.

Separate work, published in 2003 in Malaria Journal, examined what happens at cellular level — disrupted calcium homeostasis and endoplasmic reticulum stress.

Taken together, this is real evidence of a real mechanism. In rats.

What is inferred Inferred

The step from rat brainstem to human brain is where inference begins. In 2014, Dr Remington Nevin published a paper proposing that lasting effects in humans reflect permanent neuronal degeneration in specific brain regions, including the brainstem.

Confirmatory human neurohistopathological testing has never been performed. There is no human equivalent of the 2006 rat finding.

That paper was published as a Current Opinion piece — an argued position, not an experimental result. The brainstem degeneration model is demonstrated in rats and inferred in humans.

What is disputed Disputed

Two national authorities examined the evidence for long-term causation in 2017 and declined to accept it.

Australia's Repatriation Medical Authority declined in August to make Statements of Principles for chemically-acquired brain injury, citing insufficient sound medical-scientific evidence. Health Canada's safety review found no conclusive evidence of long-lasting and permanent effects.

Neither disputed that mefloquine causes serious neuropsychiatric adverse reactions. The disagreement is about how far the evidence reaches — not whether there is anything there.

Three categories, held apart

Demonstrated: brainstem degeneration in rats, described by researchers as permanent.
Inferred: a comparable process in humans — argued, not confirmed.
Disputed: whether the evidence for permanent human injury is sufficient.

An honest account holds all three at once. None of the articles that follow can be stronger than this evidence.