The absence of necrosis, mitotic activity, and the low Ki-67 proliferation index further supported the benign nature of this tumour, consistent with most previously published cases [2]. This indolent behaviour is exemplified by Satoh and Ishikawa’s 20-year follow-up of a Japanese patient with multiple PPMs, who remained asymptomatic despite slowly growing lesions, confirming the benign biological behaviour of these tumours [12]. The gene discussed is MKI67; the disease is primary progressive multiple sclerosis.