Tropical Myeloneuropathies Workup

Updated: Apr 13, 2021
  • Author: Emad R Noor, MBChB; Chief Editor: Niranjan N Singh, MBBS, MD, DM, FAHS, FAANEM  more...
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Imaging Studies

HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP)

Radiographs of the chest and myelogram are normal.

MRI of the spinal cord is indicated to rule out other causes of myelopathy and may show evidence of demyelination. Similar changes can occur in the periventricular white matter. Cord swelling or atrophy has been noted in a few cases. [13]


Other Tests

Tropical ataxic neuropathy (TAN)

Nerve conduction studies and electromyography (NCS/EMG) typically show reduction in sensory conduction velocities.

Motor nerve conduction study findings are usually normal.

Blood work including checking thiamine level, riboflavin level, albumin/total protein level, cholesterol, nicotinic acid, folate, pantothenic acid, and pyridoxine has been suggested, but there is no established diagnostic value in any of these. [14]

HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP)

Electrophysiological abnormalities often are noted below the cervical spinal cord. The most common somatosensory evoked potential study (SEP) finding is abnormal central conduction time in the lower extremity. Electric brain stimulation (caution: not approved by the US Food and Drug Administration [FDA]) often reveals abnormal motor evoked potentials. Visual and auditory evoked potentials are occasionally abnormal.

NCS/EMG usually reveals slow conduction velocity and prolonged distal latency. These findings are suggestive of a demyelinating polyneuropathy. Needle EMG often shows increased insertional activity (fibrillations and positive sharp waves) in lower thoracic paraspinal muscles.

Between 25% and 60% of patients have a mild lymphocytic pleocytosis (< 50 cells/µL) in the cerebrospinal fluid (CSF). A higher percentage have mild protein elevation. Most patients have CSF oligoclonal bands.

Patients have high titers of HTLV-1 antibodies in serum and CSF. Enzyme-linked immunosorbent assay (ELISA) or the particle agglutination method is used to detect antibodies to core, envelope, and tax viral proteins. Western blot assay can confirm the diagnosis and distinguish HTLV-1 from HTLV-2. Polymerase chain reaction (PCR) for tax and pol also can be used on peripheral blood cells and CSF cells from infected individuals. PCR is able to distinguish HTLV-1 from HTLV-2. The HTLV-1 proviral load in peripheral blood mononuclear cells is 10- to 100-fold higher than that in CSF. Patients with high proviral load and no intrathecal synthesis antibodies to HTLV-1 have more rapid progression to serious clinical disease. [15]

Urodynamic examinations reveal mainly a detrusor external sphincter dyssynergia.

Sural nerve biopsy can reveal inflammatory infiltrates, axonal degeneration, and segmental demyelination.


Histologic Findings

Tropical ataxic neuropathy (TAN)

Autopsies in a group of ex-prisoners of war revealed posterior column demyelination, particularly of the fasciculus gracilis and the optic nerves (primarily the papillomacular fibers).

Nerve biopsies in a group of Nigerian patients showed nonspecific patchy demyelination with variable pericapillary cellular reaction and perineural fibrosis.

HTLV-1–associated myelopathy/tropical spastic paraparesis (HAM/TSP)

A histopathological study of 15 Jamaican patients revealed chronic inflammation with mononuclear cell infiltration of the meninges and the gray and white matter along with proliferation of the small parenchymal vessels and perivascular cuffing (primarily lymphocytes). Demyelination was most marked in the lateral columns but also was seen in nerve roots. In the areas of most severe demyelination, the axons were relatively well preserved. The gray matter was affected to a lesser degree, although changes were sometimes observed in anterior cells. The spinothalamic and spinocerebellar tracts usually showed less severe demyelination, but when damage was severe, focal spongiosis was seen.

A detailed Japanese study of 7 autopsies revealed the same pattern of inflammation. Immunohistochemistry demonstrated T-cell dominance. The numbers of CD4 and CD8 cells were equal in patients with shorter clinical courses. CD8 cells predominated over CD4 cells in patients with prolonged clinical courses. In situ PCR demonstrated HTLV-1–infected cells exclusively in the perivascular mononuclear infiltrates.

See the images below.

Light microscopy of thoracic spinal cord of 2 pati Light microscopy of thoracic spinal cord of 2 patients with HTLV-1–associated myelopathy (Klüver-Barrera staining). (Source: Aye et al, 2000, Fig. 1.)
Light microscopy of perivascular inflammatory infi Light microscopy of perivascular inflammatory infiltration in the spinal cord (A, C) and in the brain (B, D) (A, B H&E; C, D Elastica Van Gieson; A, C x400; B, D x200). (Source: Aye et al, 2000, Fig. 2.)
Light microscopy of the middle thoracic spinal cor Light microscopy of the middle thoracic spinal cord (A, C, E) and subcortical white matter of the brain (B, D, F). Fibrotic changes are seen even in the capillaries (arrows) (A, B, F H&E; C-E Elastica van Gieson; A, C, D, F x400; B x300; E x100). (Source: Aye et al, 2000, Fig. 3.)
Immunostaining of the infiltrating cells in the th Immunostaining of the infiltrating cells in the thoracic spinal cord (A, C, E) and subcortical white matter of the brain (B, D, F) (A, B UCHL-1 [antibody to CD45RO]; C, D CD8; E, F OPD-4; A-F x150). (Source: Aye et al, 2000, Fig. 4.)
Immunostaining of the infiltrating cells in the th Immunostaining of the infiltrating cells in the thoracic spinal cord (A, C) and subcortical white matter of brain (B, D) (A, B UCHL-1[antibody to CD45RO]; C, D CD8; A-D x160). (Source: Aye et al, 2000, Fig. 5.)