Acquired equine polyneuropathy of Nordic horses: A conspicuous inclusion body schwannopathy

- Acquired equine polyneuropathy in Nordic horses is an emerging, potentially fatal disease.
- We present a case-series of in depth investigation of peripheral nerve samples and muscle biopsies of affected horses.
- We confirmed a uniform histopathological picture in all cases.
- Findings suggest an impairment of Schwannocytic protein metabolism accompanied by autoimmune events.

Acquired equine polyneuropathy (AEP), formerly also known as Scandinavian knuckling syndrome, is one of the most prevalent polyneuropathies in equids in Norway and Sweden, with more than 400 cases registered since first observations in 1995. Despite geographical clustering and an association to forage feeding, its aetiology remains unknown. Clinically AEP is characterized by knuckling due to dysfunction of metatarsophalangeal extensor muscles. This neuropathological study aimed to gain further insights in the pathobiology of AEP and its underlying aetiopathogenesis. We thereby confirmed that all affected horses suffered from similar large fibre neuropathy, exhibiting conspicuous Schwann cell inclusions in most samples, suggestive of a primary disruption of Schwann cell metabolism leading to inclusion body schwannopathy with secondary inflammatory changes. The degree of nerve pathology was not predictive of clinical outcome.