Toward a rational therapeutic strategy for arachnoiditis. A possible role for d-penicillamine. Twenty-six patients (13 men and 13 women), ranging in age from 38 to 75 years, with surgical and/or radiculographic evidence of chronic adhesive spinal arachnoiditis (CASA) were admitted to a randomly allocated, double-blind, 6-month crossover trial of d-penicillamine (500 mg/day) versus matching placebo. Assessments using subjective and objective criteria at 3-month intervals demonstrated no statistically significant effect with either d-penicillamine or placebo or between them. Thirteen of the 17 patients completing the trial expressed no clear preference. One patient preferred placebo. The remaining three patients who expressed strong preference for d-penicillamine (supported by objective data) subsequently maintained improvement on long-term therapy for up to 5 years. It is concluded that there may be a small subgroup of patients with CASA who might benefit from d-penicillamine therapy. 