Can parasites mimic Amyotrophic Lateral Sclerosis (ALS)?

Can Parasites Mimic ALS?

Yes, certain parasitic infections can mimic ALS by causing progressive motor weakness, myelopathy, and neurological deficits that resemble motor neuron disease, making them critical to exclude during the diagnostic workup.

Key Parasitic Mimics of ALS

Schistosomiasis-Associated Myelopathy

• Schistosoma mansoni and S. haematobium can cause acute myelopathy that presents with rapidly progressive transverse myelitis affecting the conus medullaris and cauda equina 1
• Clinical presentation includes lower limb pain, lower motor neuron dysfunction, bladder paralysis, and bowel dysfunction—features that overlap significantly with motor neuron disease 1
• This represents a treatable cause of progressive motor weakness that must be distinguished from ALS 1

Neurotoxocariasis

• Toxocara canis and T. cati can cause neurotoxocariasis presenting with myelitis, which may mimic the progressive weakness seen in ALS 1
• Treatment with albendazole for 3-4 weeks ± corticosteroids can reverse symptoms, unlike ALS which is progressive and irreversible 1

Cerebral Paragonimiasis

• Paragonimus westermani rarely causes myelitis that can present with motor and sensory disturbances mimicking motor neuron involvement 1
• Seizures, headache, and focal neurological deficits are more common presentations, helping differentiate from classic ALS 2

Neurocysticercosis

• Taenia solium can cause focal neurological findings and, in rare cases of spinal involvement, motor deficits 1
• However, seizures and headache are the predominant presentations, making confusion with ALS less likely 1

Critical Diagnostic Distinctions

Features Favoring Parasitic Infection Over ALS

• Eosinophilia: Parasitic infections frequently cause peripheral eosinophilia, which is not a feature of ALS 1
• Travel history: Exposure to endemic areas (tropical/subtropical regions) strongly suggests parasitic etiology 1
• Acute or subacute onset: Parasitic myelopathies often present more rapidly than the insidious progression typical of ALS 1
• Fever and systemic symptoms: May accompany parasitic infections but are typically absent in ALS 1
• Bladder and bowel dysfunction early: More prominent early in schistosomal myelopathy compared to late-stage ALS 1

Features Favoring ALS

• Mixed upper and lower motor neuron signs: Classic ALS presents with both UMN and LMN degeneration along corticospinal tracts 3, 4
• Progressive spread: ALS shows characteristic spread through contiguous body regions over months to years 5
• Absence of sensory symptoms: Pure motor involvement without sensory deficits favors ALS over parasitic myelopathy 5
• Normal inflammatory markers: Absence of eosinophilia and normal CSF (or only mildly elevated protein) supports ALS 3

Recommended Diagnostic Approach

Initial Screening for Parasitic Mimics

• Travel and exposure history: Detailed questioning about travel to endemic areas, freshwater exposure, and consumption of undercooked meat 1
• Complete blood count with differential: Check for eosinophilia, which if present, mandates parasitic workup 1
• Stool microscopy: For intestinal parasites, particularly in patients with travel history 1
• Serology: Specific antibody testing for Schistosoma, Toxocara, and other relevant parasites based on exposure history 1

Neuroimaging

• MRI head without IV contrast is the preferred initial imaging for suspected ALS to identify characteristic findings and exclude mimics 6
• MRI spine without IV contrast should be obtained when parasitic myelopathy is suspected to exclude structural, infectious, or neoplastic etiologies 1, 6
• Look for abnormal T2/FLAIR signal in corticospinal tracts (favors ALS) versus focal spinal cord lesions with enhancement (favors infection) 1, 6

When to Pursue Parasitic Workup Aggressively

• Any patient with motor symptoms AND eosinophilia requires comprehensive parasitic evaluation before diagnosing ALS 1
• Patients with travel history to endemic areas within the past 10 years (given long incubation periods for some parasites) 1
• Acute or subacute progression (weeks to months) rather than the typical insidious ALS course 1
• Prominent early bladder/bowel dysfunction disproportionate to limb weakness 1

Common Pitfalls to Avoid

• Assuming all progressive motor weakness is ALS: ALS is a diagnosis of exclusion; treatable parasitic causes must be ruled out first 5
• Overlooking remote travel history: Neurocysticercosis can present more than 10 years after initial infection 1
• Dismissing normal initial eosinophil counts: Eosinophilia may be absent in chronic or isolated CNS parasitic infections 1
• Failing to image the spine: MRI spine is crucial when myelopathy is suspected, as it can reveal parasitic lesions missed on brain imaging alone 1, 6

Treatment Implications

The distinction between parasitic infection and ALS has profound implications for patient outcomes:

• Parasitic infections are potentially curable with appropriate antiparasitic therapy (praziquantel, albendazole) and corticosteroids 1
• ALS has a mean survival of 3-5 years with only supportive care available, making misdiagnosis catastrophic 3, 4
• Early identification and treatment of parasitic mimics can prevent irreversible neurological damage 1