Unilateral plantigrade stance in piglets associated with chronic neuritis following intramuscular medication

Locomotor disorders in pigs involve both infectious and non-infectious causes; however, iatrogenic peripheral neuropathies are rare. This study describes clinical, macroscopic and histological alterations associated with an outbreak of chronic neuritis in piglets following intramuscular drug administration on two farms. In two farms, each with 500 sows, approximately 7% of farrowing house piglets (26/370) presented with a plantigrade posture of the left pelvic limb (LPL) beginning on the third day of life, with no clinical improvement despite treatment. Nine piglets were subjected to necropsy. On gross examination, an off-white thickening involving the branches of the common fibular nerve of the LPL (indicative of fibrosis) was observed. On microscopic examination, Masson's trichrome and haematoxylin and eosin staining revealed granulomatous inflammation and abundant fibrovascular connective tissue between nerve fascicles, many of which were atrophied or undergoing degeneration. The anatomopathological findings were consistent with chronic (22.2%) and chronic-active (77.8%) neuritis and perineuritis associated with denervation-induced muscular atrophy, predominantly affecting the gastrocnemius muscle, which resulted in the plantigrade posture. Considering the location and pattern of the histological lesions, as well as the history of intramuscular injections during the first days of life, the lesions were considered to be of iatrogenic aetiology.