# Clinical and Pathological Features of Flexural Deformities Associated with Myopathies in Foals

## TL;DR

This study explores muscle biopsy findings in foals with flexural deformities to better understand their underlying causes and improve diagnosis.

## Contribution

The study demonstrates the diagnostic value of muscle biopsies in identifying specific myopathies in foals with congenital flexural deformities.

## Key findings

- Muscle biopsies revealed various myopathies, including core-like myopathy and polysaccharide storage myopathy.
- Clinical symptoms alone may not distinguish between different underlying muscle disorders in foals.
- Histopathological analysis is suggested as a valuable diagnostic tool for flexural deformities in equine medicine.

## Abstract

Congenital flexural deformities (CFDs) are common in foals. The affected sites, severity of symptoms, and response to therapy vary from case to case. The etiopathogenesis is often unknown, and diagnosis is typically based on clinical examination, sometimes accompanied by radiological assessment. In contrast, children with congenital contractures require a complex diagnostic workup, which often includes a muscle biopsy. This study aimed to describe the diagnostic utility and findings of muscle biopsies in foals with flexural limb deformities. Muscle changes were observed in all assessed cases of CFDs. The most frequently identified muscle disorders included core-like myopathy, mild nonspecific myopathy, mitochondrial myopathy, polysaccharide storage myopathy, and congenital fiber-type disproportion. These findings suggest that muscle biopsy can provide valuable information for investigating congenital flexural deformities in equine medicine.

Flexural deformities (FDs) are a common condition in foals. Therapy is typically initiated without a precise diagnosis, and the etiopathogenesis often remains unknown. This study aimed (1) to investigate the clinical and pathological findings in congenital FD cases in foals and (2) to retrospectively describe the abnormalities detected in muscle biopsies of foals affected by CFDs. For these purposes, a retrospective study of the findings of muscle biopsies taken from foals with FDs referred to the Department of Veterinary Medicine and Animal Production at the University of Naples Federico II was performed from January 2005 to February 2024. Anamnesis, physical examination, hematological and biochemical data, along with the findings of histopathological muscle biopsy analysis and follow-up, were recorded. The clinical records of 15 cases of FDs were evaluated. The main clinical symptoms included flexural limb deformities associated with weakness, torticollis and scoliosis, mandibular prognathism, and inferior eyelid entropion. The evaluation of histopathological reports allowed us to observe the following muscle disorders: Core-like myopathy, mild nonspecific myopathy, mitochondrial myopathy, congenital fiber type disproportion, lipid storage myopathy, lipomatous dystrophy, myopathy with inclusion bodies, polysaccharide storage myopathy, and neurogenic myopathy. Even though many cases of FDs were diagnosed through clinical examination and successfully treated, we hypothesize that different underlying etiologies may present with similar flexural symptoms. A better understanding of these underlying causes is, therefore, desirable. These findings suggest that histopathological analysis may be a valuable tool for investigating FDs in foals, although further studies are needed to evaluate the significance of the observed alterations.