Though usually idiopathic, FSGS can occur in association with other factors (secondary FSGS), including medications and illicit drugs (eg, heroin, lithium, interferon alfa, pamidronate, cyclosporine, or nonsteroidal anti-inflammatory drugs [causing analgesic nephropathy]), atheroembolic disease affecting the kidneys, obesity, HIV infection (see HIV-associated nephropathy), and disorders causing nephron loss (eg, reflux nephropathy, subtotal nephrectomy, renal dysgenesis [eg, oligomeganephronia: renal hypoplasia with a decreased number of nephrons]).