HTLV-1-associated myelopathy, also known as tropical spastic paraparesis, is primarily seen in Japan, Melanesia and the Caribbean and presents with chronic spastic paraparesis.
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Terminology
This condition has been independently described in Japan (HTLV-1 associated myelopathy) and in the Caribbean (tropical spastic paraparesis), and it is now often referred to by both terms, i.e. HTLV-1-associated myelopathy/tropical spastic paraparesis) 1.
Epidemiology
HTLV-1 is only present in some parts of the world, endemic in Japan, and also found in the Caribbean, Melanesia, equatorial Africa, and some parts of Central and South America with an estimated 10-40 million individuals having life-long infection 1,3,4. It is transmitted by blood (transfusion, IVDU) and other bodily fluids (breastfeeding, sexual intercourse) 1,4. Despite its prevalence, only a small fraction (up to 5%) of individuals who are infected ever manifest HTLV-1 related pathology 3.
Clinical presentation
The most common neurological manifestation of HTLV-1 associated myelopathy is a chronic progressive spastic paraparesis, mainly affecting the lower limbs, with accompanying bowel and bladder dysfunction, and lower back pain 1,4-6. Sensory symptoms, if present, are often subtle, and include loss of vibration and proprioception, and paresthesias, without a well-defined sensory level 6.
A preceding episode of acute or subacute deterioration (or phase) is reported in a minority of patients 1,5. As such it is felt that there are two phases in some patients; an early acute inflammatory phase and a second chronic phase 1.
In addition of myelopathy, HTLV-1 can result in adult T-cell leukemia, encephalopathy, uveitis, keratoconjunctivitis, myositis, alveolitis and arthropathy 1,3,5.
Pathology
It is believed that HTLV-1 associated myelopathy is the result of a multifactorial immune/autoimmune response to infection with the HTLV-1 virus 1. This results in axonal and myelin loss in the cord, particularly in the lateral and posterior columns 5, although the entire cord (including grey matter) demonstrates infiltration with lymphocytes and macrophages 1.
Radiographic features
MRI is the modality of choice to evaluate spinal cord and associated cerebral manifestations. It should be noted that the MRI can be normal in many cases 8.
MRI
In chronic HTLV-1 associated myelopathy, the most common form, the hallmark radiological feature, if MRI is abnormal, is spinal cord atrophy, particularly affecting the cervicothoracic cord 2,5. This is most pronounced in the lateral and posterior columns 5, mostly involving white matter, but also involving nearby grey matter and anterior nerve roots.
In acute/subacute phases of HTLV-1 associated myelopathy, there is evidence of longitudinally extensive transverse myelitis, typically in the cervicothoracic cord, with cord swelling and high T2 signal 1,5,8. The cord swelling is often more extensive than the regions of high T2 signal 5. There may be gadolinium contrast enhancement on T1, often dorsolaterally, however, the pattern may be variable (including the trident sign and bright spotty lesions) 1,5,7.
Although the cord manifestations are the best-known features, over half of affected individuals will also demonstrate high T2 signal in the cerebral white matter, typically in the subcortical and periventricular regions 2,5. Many cases report a predilection for the paths of the corticospinal tracts 5.
Treatment and prognosis
No accepted treatment has been shown to consistently alter the disease outcome. The mainstay of treatment is immune modulation, including corticosteroids, interferon-alpha, plasmapheresis, danazol, and pentoxifylline 1,4-6.
Differential diagnosis
The differential diagnosis depends upon the phase or tempo of the disease.
In the acute/subacute phases the main differentials include:
transverse myelitis (e.g. due to neuromyelitis optica spectrum disorder (NMOSD), post-infectious, etc.) 5
In the more common chronic phase the differential includes:
multiple sclerosis, particular the primary progressive phenotype 6
HIV vacuolar myelopathy: typically posterior and lateral columns 1,4
subacute combined degeneration of the cord: typically posterior columns, but can be lateral columns
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