What are the diagnostic criteria for Neurocysticercosis (NCC)?

Diagnostic Criteria for Neurocysticercosis

The diagnosis of neurocysticercosis requires a structured approach using absolute, major, minor, and epidemiological criteria, with definitive diagnosis established by one absolute criterion OR two major plus one minor plus one epidemiological criterion. 1

Diagnostic Framework

The diagnostic criteria are stratified into four categories based on their diagnostic strength 1:

Absolute Criteria (Definitive Diagnosis with Any Single Criterion)

• Histologic demonstration of the parasite from biopsy of brain or spinal cord lesion 1
• Cystic lesions showing the scolex on CT or MRI (appears as an intracystic nodule, 1-2 mm diameter, round to slightly elongated) 1
• Direct visualization of subretinal parasites by fundoscopic examination 1

Major Criteria

• Lesions highly suggestive of NCC on neuroimaging studies (rounded parenchymal cysts 5-20 mm diameter, or racemose cysts in basal cisterns/ventricles) 1
• Positive serum enzyme-linked immunotransfer blot (EITB) for anticysticercal antibodies (this is the test of choice, NOT crude antigen ELISA) 1
• Resolution of intracranial cystic lesions after therapy with albendazole or praziquantel 1
• Spontaneous resolution of small single enhancing lesions 1

Minor Criteria

• Lesions compatible with NCC on neuroimaging studies 1
• Clinical manifestations suggestive of NCC (seizures are most common, followed by increased intracranial pressure/hydrocephalus) 1
• Positive CSF ELISA for anticysticercal antibodies or cysticercal antigens 1
• Cysticercosis outside the CNS 1

Epidemiological Criteria

• Evidence of household contact with Taenia solium infection 1
• Individuals coming from or living in cysticercosis-endemic areas 1
• History of frequent travel to disease-endemic areas 1

Degrees of Diagnostic Certainty

Definitive Diagnosis

Established in patients with:

• One absolute criterion 1, OR
• Two major PLUS one minor PLUS one epidemiological criterion 1

Probable Diagnosis

Established in patients with:

• One major PLUS two minor criteria 1, OR
• One major PLUS one minor PLUS one epidemiological criterion 1, OR
• Three minor PLUS one epidemiological criterion 1

Essential Diagnostic Workup

Neuroimaging (Mandatory)

• Both CT and MRI are recommended for complete evaluation 2
• CT is more sensitive for detecting calcified lesions 1
• MRI is more sensitive for detecting the scolex, edema, small parenchymal lesions, posterior fossa lesions, and subarachnoid/ventricular involvement 1
• FLAIR sequences are particularly helpful for identifying associated edema and the scolex 1

Serologic Testing

• Enzyme-linked immunotransfer blot (EITB) on serum is the confirmatory test of choice 1, 2
• Avoid ELISAs using crude antigen due to poor sensitivity (41%) and specificity compared to EITB (86% sensitivity) 1, 2
• Serum testing is more sensitive than CSF using EITB 1

Clinical History (Critical Elements)

Query specifically about:

• Exposure history extending months to decades prior (not just recent exposure) 1
• Access to safe water and improved sanitation throughout life 1
• Contact with tapeworm carriers (family, neighbors) 1
• Contact with pork-raising areas 1
• Consumption of undercooked pork or passage of tapeworm segments 1

Important Caveats

Differential Diagnosis Red Flags

Lesions >20 mm diameter, irregular borders, or midline shift suggest alternative diagnoses (tuberculomas, brain abscesses, tumors, lymphoma) rather than NCC 1. Presence of fever, night sweats, weight loss, or adenopathy makes NCC less likely and suggests tuberculosis or malignancy 1.

Pre-Treatment Mandatory Screening

• Fundoscopic examination is mandatory before initiating anthelmintic therapy to rule out retinal involvement 2
• Screen for latent tuberculosis in patients likely requiring prolonged corticosteroids 2
• Screen or provide empiric therapy for Strongyloides stercoralis in patients likely requiring prolonged corticosteroids to prevent hyperinfection syndrome 2

Imaging Pitfalls

Extraparenchymal cysticerci (ventricular/basal cisterns) are often not visible on CT and may only show subtle indirect findings (hydrocephalus without visible cysts, ependymitis, distorted basal cisterns) 1. The cyst membrane is thin and fluid is isodense with CSF 1.