A 58 year old female presented with progressive ambulatory dysfunction, work up showed negative serum paraneoplastic, aquaporin-4/neuromyelitis optic(NMO) and myelin oligodendrocyte glycoprotein (MOG) antibodies. CSF analysis demonstrated persistent lymphocytic pleocytosis and HTLV-1 antibody positive, on two separate occasions leading to the diagnosis of HTLV myelopathy. 

Patient was seen on follow up in the clinic with repeat MRI showing significant increase of periventricular white matter lesions and two active cerebellar lesions. Patient continued to have progressive ambulatory dysfunction but no new symptoms. The patient was presumed to have seronegative NMO being treated with IVIG, but continued to decline so IVIG was stopped. 

A year later, patient had acute gait worsening and was seen in the acute setting with significant proximal lower extremity weakness. At this time, MRI neuroaxis did not show any active lesions. The patients HTLV viral load continued to uptrend. Patient was treated with high dose steroids and plasma exchange with minimal improvement. On follow up, patient had worsening proximal lower extremity weakness despite continuous steroids and multiple rounds of plasma exchange. 

This case demonstrates an atypical progression of HAM, going from a chronic, slow progressive course to an acute rapid progression with worsening MRI brain lesions. There are no documented cases of HAM having an acute relapse superimposed on a chronic presentation. The mechanism and clinical phenotypes of HAM have limited understanding, warranting further studies to guide and advance treatment options.