Swimmer puppy syndrome, pectus excavatum, and cardiac dextroposition in two American Akitas: management and successful long-term outcome

Abstract

Swimmer puppy syndrome (SPS), also known as splay leg, splay weak, or myofibrillar hypoplasia, is an uncommon condition with poorly understood pathogenesis. It affects neonates and is characterized by sternal flattening, limb abduction, and an inability to stand or ambulate properly. This report describes two American Akita littermates diagnosed with SPS. The condition was associated with pectus excavatum and cardiac dextroposition, identified through clinical examination and thoracic imaging. Both puppies presented with persistent sternal recumbency, respiratory distress, and restricted mobility during the first weeks of life. Radiographic evaluation revealed thoracic flattening, rightward cardiac displacement, and mild pectus excavatum. A therapeutic protocol including intensive physiotherapy, active positioning, and a custom-made external thoracic splint was implemented. Marked improvement in locomotion and thoracic conformation was observed within 30 days. Long-term follow-up (two years in one case) demonstrated a successful functional outcome despite persistent, mild, rightward cardiac displacement. These observations highlight the importance of early recognition and conservative management of SPS and associated thoracic deformities.

Supplementary Information

The online version contains supplementary material available at https://doi.org/10.1007/s11259-026-11426-7.

Introduction

Swimmer puppy syndrome (SPS), also known as myofibrillar hypoplasia, is an uncommon developmental condition affecting neonatal animals and is characterised by severe locomotor impairment, persistent sternal recumbency, and limb abduction (Yardimci et al. 2009; Tomihari et al. 2022). This syndrome has been reported in dogs (Mahesh 2014), cats (Yaygingül and Tuna 2021), and rabbits (Mann et al. 2019), among other species. In dogs, it has been more frequently described in chondrodystrophic and/or brachycephalic breeds (Mahesh 2014; Karcher et al. 2018), but also in others such as Labrador Retriever (Yaygingül and Tuna 2021), Miniature Schnauzer (Kim et al. 2013), English Bulldog (Verhoeven et al. 2006), and Neapolitan Mastiff (Mahesh 2014). Reports in the American Akita breed remain scarce, with only one case described in the literature (Rumpel et al. 2023).

The aetiology of SPS remains poorly understood, with multiple proposed contributing factors including genetic predisposition, neuromuscular immaturity (such as delayed myelinization), nutritional imbalances, reduced litter size and rapid weight gain (Verhoeven et al. 2006; Kim et al. 2013; Nganvongpanit and Yao 2013; Yaygingül and Tuna 2021; Tomihari et al. 2022; Venkatesh et al. 2024). To date, no single cause has been definitively confirmed. Environmental conditions, particularly slippery or concrete floors during early development, appear to play an important role (Nganvongpanit and Yao 2013; Rumpel et al. 2023; Singh et al. 2013).

This disorder is frequently associated with pectus excavatum (PE), a sternal deformity characterised by dorsal deviation of the caudal sternebrae that causes compression of the thoracic cavity. This malformation may result in cardiorespiratory compromise and displacement of the cardiac silhouette (Rahal et al. 2008; Kim et al. 2013; Singh et al. 2013; Mann et al. 2019; Pereira et al. 2023; Moon Larson 2024). However, the association of SPS with cardiac dextroposition, as specific form of cardiac displacement, has been rarely reported in veterinary medicine.

Furthermore, the simultaneous presence of SPS, PE, and cardiac dextroposition is rarely documented in the veterinary literature. To the best of the authors’ knowledge, only a single previous report has described this combination (Anatolitou et al. 2024), where the cardiac malposition resolved following correction of the thoracic deformity. Notably, the present report provides long-term follow-up data up to two years, documenting the persistence of the abnormal cardiac position despite marked improvement in chest conformation following treatment. This observation suggests that, in these American Akitas, the displacement may not be purely secondary to the thoracic abnormality, offering further insights into the clinical heterogeneity of the syndrome.

Case reports

Two 27-day-old, female American Akita littermates (Case 1 and Case 2; 2.12 and 1.95 kg, respectively) were presented with respiratory distress, dorsoventral thoracic flattening, and an inability to stand (Fig. 1, Video S1). According to the breeder’s report, three neonates from the same litter were born with a flattened thorax. One puppy died at one week of age, while the remaining two developed progressive respiratory signs and reduced mobility. Both the sire and the dam were reportedly healthy, with no known history of thoracic deformities, locomotor disorders, or other relevant health conditions. This was the first litter produced by this breeding pair. Although neither parent underwent clinical or radiographic evaluation and no official health records were available, the breeder reported no previous history of similar abnormalities in litters produced by either parent with other mates.

Fig. 1.

Case 1 and Case 2 at presentation, showing persistent sternal recumbency and abduction of the limbs

On physical examination, both puppies were alert, with a normal coat and body condition. They exhibited persistent sternal recumbency, thoracic flattening with mild caudal depression of the sternum (more pronounced in Case 2), and limb abduction, primarily affecting the forelimbs (Fig. 1). The respiratory rate was severely increased, and both animals displayed persistent open-mouth breathing with mild effort. The tongue and oral mucous membranes were pink at rest but became pale during handling. Cardiac auscultation was unremarkable, although the apex beat was displaced caudally and toward the right hemithorax. Examination of the limbs revealed no abnormalities in muscle tone, pain, or range of motion during passive joint manipulation. Based on these findings, no specific radiographic evaluation of the limbs was performed at that time.

Obtaining lateral projections was challenging because of the puppies’ flattened thoraces, their inability to maintain lateral recumbency, and their age-related restlessness. Consequently, a lateral projection was successfully obtained in only one puppy (Case 2) using a horizontal X-ray beam while the animal was held in suspension (Fig. 2). Lateral thoracic radiograph revealed a reduced dorsoventral thoracic diameter (flattening), an intact diaphragmatic silhouette, and dorsal deviation of the xiphoid process with suspected dorsal bowing of the sternum, consistent with mild to moderate PE (Fig. 2). The dorsoventral views demonstrated cardiac dextroposition in both puppies and a pronounced pulmonary vascular pattern. Diaphragmatic integrity was confirmed, and the gastric area was normally positioned (Fig. 3). According to previous reports (Pereira et al. 2023), the frontosagittal and vertebral thoracic indices were calculated, and the severity of the deformity was assessed using these indices (Table 1).

Fig. 2.

Lateral thoracic radiograph of Case 2 at initial presentation, showing dorsoventral flattening and mild dorsal deviation of the sternum

Fig. 3.

Dorsoventral thoracic radiographs at initial presentation: A Case 1 showing cardiac dextroposition; B Case 2 showing similar cardiac dextroposition

Table 1.

Severity of pectus excavatum according to frontosagittal and vertebral thoracic indices for the available checkpoints in each puppy

	Control point	Frontosagittal index	Vertebral index	Severity
Case 1	Day 30	1.1	13.3	Mild
	6 months	1.1	13	Mild
	2 years	1	12	Mild
Case 2	Day 1	2.1	6	Moderate
	Day 30	1.1	13.3	Mild

A comprehensive echocardiographic examination was performed to further characterize the cardiac displacement. Both puppies had structurally normal hearts with appropriate chamber sizes. There was no evidence of anomalous intracardiac communications (shunts), and the inflow and outflow tracts were normal. Cardiac valves showed normal morphology and mobility. Doppler evaluation was unremarkable in both cases, except for a slight central mitral regurgitation, which was considered clinically insignificant. These findings allowed for the definitive exclusion of true dextrocardia, which is characterized by reversed base-to-apex axis.

Based on the clinical and imaging findings, both puppies were diagnosed with SPS associated with PE and cardiac dextroposition, which was more pronounced in Case 2. At this stage, however, it was not possible to distinguish whether the cardiac displacement originated from a purely positional shift (secondary to PE) or an intrinsic congenital dextroposition. Advanced imaging, such as computed tomography (CT), was not performed as it was deemed clinically unnecessary for the implementation of the chosen management protocol.

An intensive physiotherapy regimen was initiated immediately. The protocol consisted of passive range-of-motion exercises involving gentle flexion-extension of each limb joint, muscle massage for 5–10 min per session, and assisted standing stimulation on rough surfaces (e.g., grass, rubber mats) three to four times daily (Video S2). A custom-made external thoracic splint was applied and maintained throughout the 14-day treatment period. During the first 7 days, it was removed only for physiotherapy, splint adjustment, and skin inspection. Thereafter, the duration of the removal periods was progressively increased until the splint was completely removed on day 14. The external splint consisted of a PVC tube with a ventral opening beneath the sternum, intended to prevent direct sternal weight-bearing while allowing limb movement and thoracic expansion (Fig. 4). Caretakers were advised to avoid slippery floors and to ensure regular supervised re-evaluation. Hydrotherapy (supported swimming) was discussed as a potential adjunctive therapy but was not implemented. No complications, such as skin excoriations, significant stress, or respiratory compromise, were noted during the use of the splint. The breeder’s routine weaning and post-weaning feeding protocol was reviewed by the attending veterinarians and considered appropriate.

Fig. 4.

Homemade splint used to promote sternum development. Image provided by the animals’ caregivers 15 days after diagnosis. Note the constant use of rough surfaces to facilitate grip and how they are beginning to be able to stand upright

At the 30-day follow-up, both puppies showed marked improvement in thoracic conformation and locomotion (Video S3). They were able to stand and ambulate with increasing stability, and their overall activity levels had normalised. Body weights had increased to 6.1 kg (Case 1) and 5.6 kg (Case 2). Caretakers reported that continuous use of the thoracic splint during the first days was particularly critical, as it allowed the puppies to rest in lateral recumbency, thereby reducing sustained sternal compression. The use of rough, non-slippery surfaces (artificial turf) further facilitated limb support despite persistent muscle weakness. However, residual thoracic deformities persisted in both puppies. A mild sternal depression consistent with PE remained evident in Case 2, whereas Case 1 showed nearly normal thoracic conformation on follow-up thoracic radiographs (Fig. 5; Table 1). Both puppies continued to exhibit rightward displacement of the cardiac silhouette, although this was less pronounced than at the initial presentation, particularly in Case 1 (Fig. 6). Three months after the initial diagnosis, both puppies exhibited virtually nearly normal mobility (Video S4).

Fig. 5.

Lateral thoracic radiographs after 30 days of treatment: A Case 1 showing improvement of thoracic proportions (less dorsoventral flattening); B Case 2 showing mild pectus excavatum

Fig. 6.

Dorsoventral thoracic radiographs after 30 days of treatment: A Case 1 showing cardiac dextroposition; B Case 2 showing pronounced cardiac dextroposition

At the six-month and two-year follow-up examinations, only Case 1 was available for re-evaluation. The dog displayed normal activity and exercise tolerance, notwithstanding occasional slipping and mild external rotation of the forelimbs during standing (Fig. 7). Echocardiographic findings remained within normal limits. Thoracic radiographs demonstrated a persistent, albeit reduced, cardiac displacement. Routine haematology and serum biochemistry revealed only mild, clinically insignificant abnormalities. Overall, thoracic conformation and limb alignment exhibited significant and sustained improvement (Figs. 8 and 9).

Fig. 7.

Case 1 on the checkpoint 6 months after diagnosis. Note positioning with elbows excessively abducted in sternal decubitus (A) and showing elbows medial rotation while standing (B)

Fig. 8.

Thoracic radiographs of Case 1 six months after presentation: A lateral projection; B dorsoventral projection

Fig. 9.

Thoracic radiographs of Case 1 two years after presentation: A lateral projection; B dorsoventral projection

Discussion

Puppies affected by SPS typically exhibit impaired mobility and balance during the neonatal period, resulting in lateral limb extension and the characteristic paddling movement (Yardimci et al. 2009; Nganvongpanit and Yao 2013). While brachycephalic and chondrodystrophic breeds are traditionally considered more predisposed (Mahesh 2014; Karcher et al. 2018), this report documents its occurrence in two American Akita littermates. As this breed is not typically associated with this syndrome, these cases highlight significant variability in both clinical presentation and breed distribution. The clinical novelty of these cases stems from the concurrent presentation of SPS, PE, and cardiac dextroposition, underscoring the complexity of this clinical triad.

The clinical presentation observed in both puppies aligns with previous reports (Hoskins 2001; Verhoeven et al. 2006; Kim et al. 2013; Nganvongpanit and Yao 2013; Singh et al. 2013; Mahesh 2014; Karcher et al. 2018; Mann et al. 2019; Pereira et al. 2023; Anatolitou et al. 2024; Moon Larson 2024; Venkatesh et al. 2024). Cardiac dextroposition is rarely reported in association with SPS and in these cases persisted despite thoracic remodelling, representing a notable feature when compared to previously published reports. In SPS, the hind limbs are predominantly affected, either in isolation or alongside the forelimbs. However, exclusive forelimb involvement, as noted in these two cases, is considered rare (Nganvongpanit and Yao 2013), further emphasising the heterogeneity of SPS.

Both puppies exhibited PE, a thoracic deformity previously described as either an independent condition or in association with SPS (Verhoeven et al. 2006; Kim et al. 2013; Moon Larson 2024). In the present cases, PE was regarded as a consequence of prolonged sternal recumbency rather than a primary cause of the syndrome. This hypothesis aligns with reports suggesting that sustained pressure on the immature neonatal thorax can lead to skeletal remodelling (Hoskins 2001; Nganvongpanit and Yao 2013; Karcher et al. 2018; Venkatesh et al. 2024). The nature of cardiac displacement in patients with PE is traditionally considered positional, a mechanical consequence of the sternal intrusion into the thoracic cavity (Singh et al. 2013; Mann et al. 2019; Moon Larson 2024). However, the persistence of cardiac dextroposition in these American Akitas, documented up to two years, despite successful thoracic remodelling and a normal-shaped chest, may suggest an intrinsic congenital origin rather than a secondary mechanical shift. The association between SPS and cardiac dextroposition has rarely been reported in veterinary medicine, making this finding a notable feature of these cases. Nevertheless, we acknowledge that the lack of advanced imaging (CT) and the limited number of cases (n = 2) make this interpretation suggestive rather than definitive and represent a potential limitation of our data.

The aetiology of SPS remains poorly understood and is considered multifactorial. Proposed contributing factors include delayed myofibrillar development and rapid weight gain, as well as nutritional, neurological, hereditary, orthopaedic, metabolic, and environmental influences such as slippery floors (Verhoeven et al. 2006; Kim et al. 2013; Nganvongpanit and Yao 2013; Yaygingül and Tuna 2021; Tomihari et al. 2022). In the present report, both affected puppies were from the same litter and were raised under identical environmental conditions; additionally, a third littermate was reportedly affected but died before clinical evaluation. The occurrence of this syndrome in multiple littermates in a breed where SPS is rarely documented suggests and underlying hereditary or breed-related component in the American Akita, potentially interacting with environmental triggers. However, definitive conclusions cannot be drawn from this limited sample size.

Historically, SPS was considered untreatable, and euthanasia was even considered (Verhoeven et al. 2006). More recently, conservative management strategies have been associated with favourable outcomes, although a standardised treatment protocol is still lacking (Yardimci et al. 2009; Venkatesh et al. 2024). The therapeutic approach employed, based on intensive physiotherapy and external thoracic support, has been previously described (Yardimci et al. 2009; Kim et al. 2013; Mahesh 2014; Anatolitou et al. 2024). Additional measures, such as muscle massage and active positioning on rough surfaces, were also applied without complications. These findings highlight the importance of early, intensive, and multimodal conservative management.

Despite the overall positive outcome, mild residual abnormalities persisted, including a subtle external rotation of the forelimbs in Case 1. Abnormal limb positioning and uneven load distribution may predispose affected joints to chronic biomechanical stress and inflammation (Rychel 2010), potentially increasing the risk of osteoarthritis as the body attempts to stabilise the joint. Therefore, SPS may have long-term musculoskeletal implications, underscoring the importance of continued orthopaedic monitoring in affected animals. Early identification of abnormal limb alignment may allow for timely intervention to minimise the risk of secondary complications.

A limitation of present report is the inconsistency in long-term follow-up. While both puppies showed identical clinical improvement at 30 days, only Case 1 was re-evaluated at six months and two years, as Case 2 was lost to follow-up. This limitation prevents the generalisation of the long-term successful results to both animals, making our two-year observations strictly applicable to Case 1.

Preventive measures remain largely empirical due to the limited understanding of SPS pathogenesis. Until further evidence is available, the selection of breeding pairs without a history of SPS or thoracic deformities, the use of non-slippery surfaces during early development, and close neonatal monitoring are advisable (Kim et al. 2013; Nganvongpanit and Yao 2013; Singh et al. 2013). If SPS is identified in one puppy, the evaluation of the remaining littermates is recommended (Karcher et al. 2018).

This report documents the rare presentation of SPS associated with PE and cardiac dextroposition in two American Akita littermates. Early intensive physiotherapy combined with environmental modification and external thoracic support resulted in substantial functional improvement. Although mild cardiac displacement persisted, the long-term outcome in the monitored patient was favourable. Early recognition and conservative management appear critical to optimise the prognosis in affected puppies.

Supplementary Information

Below is the link to the electronic supplementary material.

Video S1. Clinical presentation at initial examination.

Video S2. Physiotherapy protocol.

Video S3. Thirty-day re-evaluation.

Video S4. Three-month follow-up.

Author contributions

Conceptualization, J.T.L.; methodology, J.T.L. and M.S. validation, J.T.L., E.H.R. and M.S.; formal analysis, J.T.L., E.H.R. and M.S.; investigation, J.T.L., E.H.R. and M.S.; resources, J.T.L. and M.S.; data curation, J.T.L., E.H.R. and M.S.; writing—original draft preparation, E.H.R; writing—review and editing, J.T.L., E.H.R. and M.S; visualization, J.T.L., E.H.R. and M.S; supervision, J.T.L. and M.S; project administration, J.T.L.; funding acquisition, J.T.L. and M.S. All authors have read and agreed to the published version of the manuscript.

Funding

Open Access funding provided thanks to the CRUE-CSIC agreement with Springer Nature.

Data availability

No datasets were generated or analysed during the current study.

Declarations

Ethical statement

Owner consent was obtained for clinical management and publication of these cases. Ethical approval was not required due to the retrospective nature of the report.

Competing interests

The authors declare no competing interests.