Hereditary causes:
(1) Oliver-McFarlane Syndrome
(2) oculocutaneous albinism type I
(3) familial hypertrichosis
Acquired disorders:
(1) systemic lupus erythematosus
(2) dermatomyositis
(3) HIV disease
(4) paraneoplastic disorder (renal cell carcinoma, other)
(5) uveitis
Drug-induced causes:
(1) interferon-alpha
(2) topiramate (an anticonvulsant)
(3) tacrolimus, cyclosporine or other immunosuppressive agents
(4) EGFR tyrosine kinase inhibitors
(5) recombinant antibody to EGFR (cetuximab)
(6) topical antiglaucoma (hypotensive) agents
If hereditary then other family members should have long eyelashes.
If drug-induced then the onset should be after the drug was started and discontinuation of the drug should result in reversal of the change.