A prospective study of neurocognitive changes 15 years after chronic inhalant abuse.

Aims: In a previous study, neurological and cognitive deficits reflecting central nervous system (CNS) disruption from chronic inhalant abuse showed substantial recovery after 2 years' abstinence. Functional recovery was progressive, with recovery rates dependent on the degree of impairment prior to abstinence, and severity and duration of initial abuse. Persistent deficits occurred in those with previous 'lead encephalopathy' from leaded petrol abuse. The current study examined recovery in the same cohort 15 years after baseline.

Design: Prospective cohort design.

Setting: Two remote Aboriginal communities in Arnhem Land, Australia.

Participants: Using baseline group classifications, 27 healthy controls, 60 ex-chronic inhalant abusers and an additional 17 with previous lead encephalopathy were assessed.

Measurements: Standard neurological, ocular-motor and cognitive functions and blood lead levels.

Findings: Chronic (non-encephalopathic) inhalant abusers showed elevated blood lead levels and abnormal scores on most tasks at baseline. At 2 years' abstinence, blood lead was reduced but remained elevated and most scores had normalized. By 15 years, blood lead and all performance scores were equivalent to healthy controls for this group (P > 0.05). The encephalopathic group was more severely impaired on all scores at baseline and showed little improvement, if any, across all tests after both 2 and 15 years' abstinence. Blood lead for this group declined, and was not significantly different to controls after 15 years.

Conclusions: Some inhalant abusers experience severe and persistent neurological deficits, suggesting irrecoverable damage attributable to lead encephalopathy. In the absence of this encephalopathy long-term abstinence from inhalants may allow recovery of normal brain function.