An acute onset of neuromuscular weakness associated with some of the arboviral infections
aresuch as Dengue fever,[1] Chikungunya fever, West Nile encephalitis, Japanese encephalitis.
Clinical examination plays an important role in diagnosis of neuromuscular weakness.
Specific findings include muscle wasting or swelling, muscle tenderness, fasciculations
or myokymia, myotonia, presence of tendon reflexes, and skin lesions. Electrophysiological
studies like EEG can pinpoint the involvement of CNS in arboviral infections[2]. A
biopsy of nerve or muscle and ancillary investigations, namely EMG, NCV, can be invaluable
in typing and sub-classifying the neuromuscular pathology. Advanced radiological techniques
like magnetic resonance imaging (MRI), PET scan or fMRI (functional MRI) of the brain
and spinal cord need to be done when there is a suspicion of upper motor neuron involvement.
Virus isolation as a gold standard should be attempted in susceptible cell lines,
namely C6/36, Vero, BHK-21, LLC-MK2. If any cytopathic effect (CPE) is observed then
it should be characterised by molecular diagnostic techniques like RT- PCR. Serological
confirmation should be done by MAC-ELISA, NS1 ELISA.[3] Immunocytochemistry should
also be performed to show localization of viral antigens in muscle tissue/skin.
West Nile Virus (WNV) is known to produce a meningo-encephalitis with an acute flaccid
paralysis.[4] Severe WNV infection can also mimic Guillain-Barré syndrome (GBS) but
is differentiated by fever; encephalopathy; predominantly proximal, asymmetric weakness;
axonal pathology on nerve conduction studies;[5] and cerebrospinal fluid variables.
The cerebrospinal fluid typically shows lymphocytic pleocytosis with elevated proteins.
Enzyme-linked immunosorbent assay for immunoglobulin IgM antibody to WNV is highly
sensitive and should be considered. As IgM antibodies can persist for up to a year
after primary infection, serial IgM titers or IgG avidity studies can help to differentiate
primary infection from past infection. MRI may show enhancement of the cauda equina,
spinal cord signal changes, and cerebral parenchymal or leptomeningeal signal changes.
Treatment is mainly supportive, and no antiviral medications have any proven benefit
in the management of WNV.
Immunohistology on muscle biopsies from chikungunya virus-infected patients with myositic
syndrome showed that viral antigens were found exclusively inside skeletal muscle
progenitor cells (designed as satellite cells) and not in muscle fibers. Muscle cells
have been proposed to be target cells for alphavirus infection. However, these studies
were either performed on animal models, or only based on clinical observations in
man, and the cellular target of virus infection was either not identified within the
muscle, or identified as muscle fibers and/or infiltrating cells.[6] Cases of GBS
have been described in association with the arboviruses such as Dengue and West Nile
and also with Chikungunya virus.
The electrolyte disorders mainly potassium imbalance are among the most common causes
that produce neuromuscular weakness. Recurrent muscular weakness is caused by hypokalemic
periodic paralysis or thyrotoxic periodic paralysis. Generally, patients with hypokalemic
periodic paralysis do not lead to respiratory failure. Acquired hypokalemia from causes
such as diarrhea or gastroenteritis can also produce muscular weakness and respiratory
failure.[7] The patients with serum potassium levels less than 3.5 mEq/L require oral
or intravenous potassium infusion. Potassium should be co-administered only with normal
saline as glucose infusions further depletes potassium ions leading to severe hypokalemia.
Other, more rarely, severe hypophosphatemia can cause muscular weakness.[8]
If the presence of myopathy is uncertain, electromyography may be indicated. Although
changes seen on electromyography are not pathognomonic for any specific disease process,
an abnormal electromyogram can indicate if a neuropathy or neuromuscular disease is
present or can help solidify the diagnosis of a primary myopathy. Muscle inflammation,
atrophy, necrosis, denervation, or neuromuscular disease can alter these components,
giving rise to patterns that may help illuminate the underlying pathology.
If the diagnosis is still inconclusive after the history, physical examination, and
laboratory, radiologic, and electromyographic evaluations, a muscle biopsy is required
for patients who have a suspected myopathy. The technology of this method, especially
regarding the use of genetic markers, is advancing rapidly, making a definitive diagnosis
possible for a wider range of myopathies.
Clinicians must therefore consider arboviral infections as an important cause of neuromuscular
weakness which must be corroborated by virological studies, namely serology, virus
isolation and PCR, in view of emerging and re-emerging viral infections.