Table 1. Serologic results for West Nile virus (WNV)–specific antibodies in patients with acute flaccid paralysis associated with acute WNV infectiona IgM-capture enzyme immunoassay Case no. Onset Collection Sample SLEV WNV 1 6/24 7/12 Serum 3.5 22.3 2 7/12 7/16 Serum 8.0 22.7 3 7/26 8/1 Serum 2.79 24.9 4 7/29 8/3 Serum 1.1 14.1 4 7/29 8/3 CSF 3.3 39.2 4 7/29 8/13 Serum 4.4 23.5 5 8/11 8/15 Serum 2.02 5 8/11 8/29 Serum 3.4 25.7 6 8/13 8/16 CSF 6.1 23.8 6 8/13 8/16 Serum 1.0 5.7 7 9/1 10/24 Serum 2.8 10.6 7 9/1 9/6 CSF Not performed 7.4 aIgM, immunoglobulin M; SLEV, Saint Louis encephalitis virus; CSF, cerebrospinal fluid. Plaque reduction neutralization assay SLEV WNV 320 5,120 80 1,280 <10 640 <10 80 40 <10 10 RESEARCH 2,560 40 320 history of fever, chills, night sweats, myalgias, and acute encephalopathy. Neurologic examination showed pro- found weakness in both arms, asymmetric weakness in the legs with a right foot drop, and acute respiratory distress (Table 2). Sensory test results were normal. Although com- puted tomography (CT) and magnetic resonance imaging (MRI) of the brain showed normal results, heparin was administered for suspected evolving stroke. Admission laboratory values (Table 3) showed serum leukocytosis, and cerebrospinal fluid (CSF) obtained on day 3 showed elevated protein. By day 8, Guillain-Barré syndrome was suspected, and intravenous immunoglobulin (IVIG) was administered. Electrodiagnostic studies performed that day were interpreted as showing a proximal neuropathy or myopathy. A deltoid muscle biopsy for suspected inflam- matory myopathy showed mild type 2 fiber atrophy but no obvious necrosis or marked inflammatory response. On day 30, the patient was transferred for rehabilitation with flaccid, areflexic paralysis in the right leg and variable weakness and diminished reflexes in all other limbs. Neck flexors were normal in strength, and sensation was pre- served in all limbs; loss of bladder function was evident. MRI of the cervical spine showed normal results. Electrodiagnostic studies showed widespread but variable denervation, reduced compound muscle action potentials (CMAPs), and normal sensory nerve action potentials (SNAPs), consistent with a severe, asymmetric process affecting anterior horn cells or motor axons. Myopathy, demyelinating polyneuropathy, and diffuse axonal polyneuropathy were not evident. Case 2 On July 15, 2002, a 57-year-old male Mississippi resi- dent with a remote history of prostate cancer and glucose intolerance was hospitalized with a 3-day history of fever, chills, nausea, vomiting, and headache. Neurologic exam- ination showed encephalopathy and asymmetric weakness in all limbs (Table 2). Results of a brain MRI weree nor- mal. Admission laboratory studies showed a CSF pleocy- tosis with elevated protein (Table 3). On day 5, acute res- piratory distress developed, and the patient required mechanical ventilation. Upon extubation 2 weeks later, the patient had continued extremity weakness and was aspirat- ing fluids; a modified barium swallow study showed oropharyngeal dysphagia. Upon transfer to a rehabilitation center on day 30, the patient had asymmetric weakness in the legs and right arm and moderate weakness in neck flex- ors and facial muscles. Hypotonia and areflexia were noted in all limbs. Sensation was slightly diminished to vibration and proprioception in toes bilaterally but preserved to light touch, pinprick, and temperature. Sensory testing was nor- mal in the upper limbs. Urinary incontinence was noted. Table 2. Initial clinical signs and symptoms in patients with acute flaccid paralysis associated with acute West Nile virus infection Case no. Fever (>38.5°C) Headache Nuchal rigidity Altered mental status Tremor Distribution of weaknessa 1 + + + + + Upper and lower limbs, R > L 2 + + - + - Upper and lower limbs, R > L 3 + - - - + Lower limbs, R > L 4 + + + + + R upper limb 5 - + - - - R upper limb 6 + + - - + Lower limbs, R > L 7 + + + - - Upper and lower limbs, L > R; bulbar muscles aR, right; L, left. Emerging Infectious Diseases • Vol. 9, No. 7, July 2003 789