They also found that being a pony, having an adequate body condition score and being treated with pergolide were associated with survival. Laminitis was diagnosed in 89.9% of cases and insulin dysregulation was diagnosed in 76.5% of cases in which they were investigated (note that horses with chronic laminitis may have had previous but not necessarily current insulin dysregulation, so it is possible for horses with signs of laminitis to not test positive to insulin dysregulation - earlier testing before or at the time of the first laminitic changes might have identified insulin dysregulation).
Horn R, Bamford NJ, Afonso T, Sutherland M, Buckerfield J, Tan RHH, Secombe CJ, Stewart AJ, Bertin FR
Factors associated with survival, laminitis and insulin dysregulation in horses diagnosed with equine pituitary pars intermedia dysfunction
Equine Veterinary Journal published online 12 November 2018 https://doi.org/10.1111/evj.13041
Equine Cushing's Disease: Australian and North American Differences - KER Dec 2018