A dysfunction of the blood-CSF barrier, i.e. abnormal elevation of Q-Alb, occurs in various neurological diseases of inflammatory as well as noninflammatory aetiology. While mild-to-moderate Q-Alb elevations (8–25 × 10⁻³) are seen in many diseases such as diabetic and immune-mediated polyneuropathies (PNP), viral meningitis or vertebral disc pathologies, moderate-to-severe Q-Alb elevations (>25 × 10⁻³) are associated with a purulent meningitis, acute Lyme neuroborreliosis, neurotuberculosis, immune-mediated polyradiculitis and myelitis or severe spinal canal stenosis.

Among patients with PNP, no significant correlation was found between duration of disease and extent of Q-Alb. There was also no significant difference between subtypes of PNP as classified by electroneurography or by underlying aetiology such as diabetes, vitamin B12 deficiency and others (Brettschneider et al. 2005) (Table 9.1).