Tongue atrophy as a neurological finding in hereditary polyneuropathy in Alaskan malamutes

Abstract

Background: Tongue atrophy with wrinkling as a clinical sign of inherited polyneuropathies has not been reported in dogs.

Objectives: Clinically describe tongue atrophy as well as morphology of the tongue and hypoglossal nerve in Alaskan malamute polyneuropathy (AMPN).

Animals: Six client-owned Alaskan malamute dogs diagnosed with AMPN, all homozygous for the causative mutation in the N-myc downstream-regulated gene 1 (NDRG1) and 1 neurologically normal control Alaskan malamute.

Methods: Prospective case study. Clinical and neurological examinations were performed on affected dogs. Necropsy samples from the tongue muscle and hypoglossal nerve were examined by light and electron microscopy.

Results: All affected dogs had abnormal wrinkles and grooves on the dorsal surface of the tongue, a clinical sign not described previously in dogs with AMPN. Electromyography of the tongue performed in 2 dogs showed spontaneous activity. Five affected dogs underwent necropsy studies. Histopathology of the tongue showed groups of angular atrophic myofibers and changes in the hypoglossal nerve included thinly myelinated fibers, small onion bulbs, folded myelin, and axonal degeneration.

Conclusion and clinical importance: Histopathologic changes in the tongue and hypoglossal nerve were consistent with previously reported changes in skeletal muscle and other nerves from dogs with AMPN. Therefore, we conclude that macroscopic tongue atrophy is part of the disease phenotype of AMPN and should be considered a potential clinical sign in dogs with polyneuropathies.

Keywords: Alaskan malamute polyneuropathy; Charcot-Marie-Tooth type 4D; NDRG1 mutation; hypoglossal nerve.