Assessment of the cutaneous trunci muscle reflex in healthy cats: comparison of results acquired by clinicians and cat owners

Abstract

Objectives

The study aimed to evaluate the cutaneous trunci muscle reflex (CTMR) in healthy cats using methods performed by the clinician and the cat’s owner at home.

Methods

A total of 55 healthy cats without neurological abnormalities were included in this study. CTMR evaluation was performed sequentially in each cat using three methods by a clinician: method A, pinch skin with a straight 14 cm Crile haemostat forceps; method B, displace fur with the tip of a pen or haemostat forceps; and method C, poke skin with the tip of a straightened paper clip. The normal response rates for each method were obtained and compared. A ‘CTMR performance score’ was assigned for each cat, reflecting the presence of a normal CTMR response using one or more of the three methods. An ‘owner performance score’ was also obtained, reflecting the response of the CTMR when performed at home by the cat owner. The two scores were compared as paired data for each cat.

Results

The CTMR was elicited normally in 17 (31%), 27 (49%) and 16 (29%) cats using methods A, B and C, respectively. Method B delivered a significantly higher percentage of normal responses. When comparing the ‘CTMR performance score’ and ‘owner performance score’, the percentage of normal responses was 60% and 100%, respectively, which was significantly different.

Conclusions and relevance

The overall normal response rate of the CTMR in healthy feline subjects was low when performed by a clinician, regardless of the method applied. Conversely, a high percentage of normal responses was obtained by cat owners performing CTMR at home, potentially indicating the impact of stress on the CTMR performance.

Introduction

The cutaneous trunci muscle reflex (CTMR) is an intersegmental reflex. The afferent information is conveyed via the cutaneous nerves, and motor neurons in the ventral horn of the C8 and T1 spinal segments conduct efferent information to the cutaneous trunci muscle via the lateral thoracic nerve. ¹ When assessing the CTMR, the suggested sensory stimulus is a mild compression of the skin of the trunk using forceps, starting in the caudal lumbar region and progressing cranially along the dorsal midline of the trunk. ² The examiner should watch for a motor response of a brief contraction of the bilateral cutaneous trunci muscle, causing the overlying skin to twitch.

DeLahunta et al mentioned that the cutaneous trunci reflex might not be elicited in some healthy dogs and cats, and variation exists regarding where the muscle contraction first appears. ² The CTMR has recently been assessed in healthy and neurologically abnormal cats.^3,4 In the 65 healthy cats tested, the CTMR could be elicited bilaterally in 80% of cats and unilaterally in 98% of cats with both instruments. When comparing the results by performing the CTMR with a haemostat or the integrated Babinski tip of an MDF Babinski Buck Reflex Hammer, the former instrument elicited the reflex further caudally and usually bilaterally.

According to our clinical observation, the percentage of feline patients in which the CTMR can be elicited is subjectively lower than that reported in previous studies. In addition, performing the CTMR with a haemostat does not seem to be the most effective method. Lastly, to the best of our knowledge, the impact of stress on the reliability of the CTMR has not been assessed previously. This study aimed to assess the CTMR performed by the clinician using three different methods in healthy cats from the Taiwan feline population. In addition, these results were compared with the CTMR performed by the owner at home to evaluate the impact of stress on the CTMR.

Materials and methods

The inclusion criteria were cats aged over 6 months, that were in good general health and had no history or clinical evidence of neurological diseases. The enrolled cats were owned by staff or students at the National Taiwan University Veterinary Hospital (NTUVH) or laypeople. The Institutional Animal Care and Use Committee (NTU-104-EL-00076) approved the study protocol.

Depending on the owner’s preference, the first part of the study was conducted either in a consultation room at the NTUVH or the owner’s home. All cats had an acclimatisation period of 5–10 mins in the room with the examiner prior to manipulation. The owners also accompanied the cats throughout the procedure. A physical examination was performed, and cats were excluded if they were dehydrated or appeared to be ill. The breed, age, sex, neuter status, body condition score (BCS; Nestlé Purina Body Condition System), the examination location and whether they displayed signs of aggression during manipulation (eg, hissing, growling, biting or hitting/scratching the examiner) were recorded.

A single examiner (CYT) performed the complete neurological examination on all cats. The CTMR was evaluated sequentially by three different methods: method A, pinch skin with a straight 14 cm Crile haemostat forceps; method B, displace fur with the tip of a pen or haemostat forceps; and method C, poke skin with the tip of a straightened paper clip (see video in the supplementary material). Stimulation was started at the level of the iliac crests, 1–2 cm lateral to the dorsal midline. Stimulation was advanced 1 cm at a time until a CTMR was elicited or stopped at the scapula level if the reflex was not elicited the whole way. The location to elicit the CTMR was recorded as the corresponding spinous process parallelly or just cranially. Details of the abnormal responses were recorded.The owners were also taught how to perform the CTMR and recognise its normal response.

The cat owner was instructed to perform the CTMR at home by themselves with any of the three methods mentioned above, at least 24 h after the complete neurological examination conducted by the author. The results were reported verbally and recorded as normal or abnormal.

For statistical analysis, the results of the CTMR were recorded as normal if the CTMR could be elicited at the level of the iliac crests bilaterally and were recorded as abnormal for any other response. The normal response rates of the three methods were compared using Cochran’s Q test, followed by post-hoc analysis if indicated.

For each cat, a ‘CTMR performance score’ was assigned. If any of the three methods could elicit a normal CTMR, it was scored as 1. If the CTMR could not be normally elicited with any of the three methods, it was scored as 0. The correlation between CTMR performance score and the sex (male/female), aggressiveness (yes/no) and the examination location (hospital/home) was analysed using the χ² test. After performing Shapiro–Wilk’s test, the relationship between the CTMR performance score and age was tested using Kendall’s tau-b test. The association between the CTMR performance score and BCS was tested using the Cochran Armitage test.

Lastly, in the cats in which the CTMR was re-tested by the owners at home, the results were recorded as the ‘owner performance score’ (score 1 for normal response and 0 for abnormal response). The ‘owner performance score’ was paired with the CTMR performance score for each cat, and the difference between the two scores was compared using the McNemar test.

All statistical analyses were performed using SPSS version 20. Statistical significance was set at P <0.05.

Results

A total of 55 cats were enrolled, representing eight breeds (39 domestic shorthairs, one American Shorthair, one British Shorthair, two Bengals, four Persians, one Scottish Fold, one Siamese and six mixed-breed cats). The age ranged from 1 to 10 years (mean 4.3). Of the cats, 25 were female (6 intact, 19 spayed) and 30 were male (6 intact, 24 castrated). The BCS was in the range of 3–8 (median 5). A complete neurological examination performed by the author was conducted at NTUVH on 34 (62%) cats and in the owner’s home on 21 (38%) cats. The CTMR was repeated at home by 52 owners, of which 43 (83%) were staff or students at NTUVH.

The CTMR was elicited normally in 17 (31%), 27 (49%) and 16 (29%) cats, using methods A, B and C, respectively. The CTMR was elicited normally with all three methods in only 7 (13%) cats. Figures 1 and 2 show the distribution of responses between and within each method. Table 1 summarises the abnormal responses for each method.

Figure 1.

Venn diagram of cats with a normal cutaneous trunci muscle reflex (CTMR) evaluated by three methods. The CTMR was elicited normally in 17, 27 and 16 cats, using methods A, B and C, respectively. In only seven cats, the CTMR was elicited normally with all three methods. Method A = pinch skin with haemostat forceps; method B = displace fur with the tip of a pen or haemostat forceps; method C = poke skin with the tip of a straightened paper clip

Figure 2.

Distribution of cutaneous trunci muscle reflex (CTMR) results regarding methods A, B and C. Normal = the CTMR was elicited at the level of the iliac crests bilaterally; bilaterally absent = unable to elicit a CTMR along the whole dorsum on both sides; other = abnormal CTMR other than bilaterally absent

Table 1.

Description of abnormal cutaneous trunci muscle reflex (CTMR) responses regarding methods A, B and C

Method and description of abnormal responses		n
A	Unable to elicit a CTMR along the whole dorsum on both sides	35
A	Normally elicited on one side; unable to elicit a CTMR along the whole dorsum on the other side	3
B	Unable to elicit a CTMR along the whole dorsum on both sides	25
B	Normally elicited on one side; unable to elicit a CTMR along the whole dorsum on the other side	3
C	Unable to elicit a CTMR along the whole dorsum on both sides	28
C	Normally elicited on one side; unable to elicit a CTMR along the whole dorsum on the other side	4
C	Normally elicited on one side; cutoff cranial to L6 on the other side	2
C	Unable to elicit a CTMR along the whole dorsum on one side; cutoff cranial to L6 on the other side	4
C	CTMR cutoff at T10 on one side, at T11 on the other side	1

A significant difference (P = 0.014) was detected between the normal response rates of the three methods. Post-hoc analysis indicated that method B (‘displace fur with the tip of a pen or haemostat forceps’) delivered a significantly higher normal response rate than method A (P = 0.025) and method C (P = 0.049).

A total of 22 (40%) cats had a CTMR performance score of 0 (CTMR could not be normally elicited with any method). When comparing the distribution of CTMR performance scores, there were no significant differences regarding the sex, aggressiveness of the cat or the examination location (Table 2). There was no correlation between the CTMR performance score and the age or BCS.

Table 2.

Results of cutaneous trunci muscle reflex (CTMR) performance score analysis regarding sex, aggressiveness of the subject and location of performing CTMR

		CTMR performance score
		Score 1	Score 0	P value
Sex	Male	18 (60)	12 (40)	1.0
	Female	15 (60)	10 (40)
Aggressiveness	Yes	8 (47)	9 (53)	0.19
	No	25 (65.8)	13 (34.2)
Location	Hospital	23 (67.6)	11 (32.4)	0.141
	Home	10 (47.6)	11 (52.4)

Data are n (%)

Score 1 = A normal CTMR could be elicited by any one of the three methods; score 0 = CTMR could not be elicited with any of the three methods

In the 52 cats whose owners additionally performed the CTMR at home, the results were recorded as normal in all 52 (100%) cats. Among these 52 cats, the previous CTMR performance score was recorded as 0 in 19 (37%) cats. Furthermore, regardless of the location of the examination, the original CTMR performed by the author was scored as 0 in 32–44% of cats (Table 3). The proportion of scores 1 and 0 in the ‘owner performance score’ and the ‘CTMR performance score’ was significantly different (P <0.001).

Table 3.

Cutaneous trunci muscle reflex (CTMR) performance score and location of the original CTMR performed by the author in the 52 cats in which the owners additionally repeated the CTMR at home

	Original CTMR performed by the author
	In the hospital (n)	At the owner’s home (n)
CTMR performance score 1	23	10
CTMR performance score 0	11	8

Score 1 = a normal CTMR could be elicited by any one of the three methods; score 0 = CTMR could not be elicited with any of the three methods

Discussion

The CTMR is an intersegmental reflex postulated to protect the skin from irritant stimuli. ¹ The CTMR has been integrated into neurological examinations in dogs and cats to aid lesion localisation, especially for patients with T3–L3 myelopathy. ⁵

The sensory field and repeatability of the CTMR in healthy dogs were previously evaluated. The caudal border of the CTMR reflex was bilaterally symmetrical in 153/155 dogs. ⁶ The CTMR was also evaluated in healthy cats by Foss et al ³ with two different instruments. When using the haemostats, the caudal border of CTMR was identified in 60/65 cats. The CTMR was present bilaterally in 58 cats and symmetrically in 38 cats. Furthermore, the caudal border was at L6 or L7 in 42 cats.

In our study, we tested the normal response rate of the CTMR using three methods. The normal response rate was significantly higher with method B, ‘displace fur with the tip of a pen or haemostat forceps’. Nevertheless, all three methods displayed a low–normal response rate of <50%. For method A, ‘pinch skin with haemostat forceps’, the normal response rate was only 31%. Although it is difficult to compare our results with the previous study by Foss et al ³ using the exact definition, a discrepancy was still noted. The reason for such variable results is unknown. Differences in the strength, location of testing and amount of pinched skin may have been present between studies. Although both studies recruited healthy feline subjects, and the majority were domestic shorthair cats, we are aware that the general temperament and lifestyle of cats in Taipei City might differ from those in the USA. Most cats enrolled in the current study were often kept strictly indoors, seldom interacted with animals or humans other than those within the family and were timid, anxious or even aggressive when taken outdoors or when encountering strangers. These innate characteristics may influence the performance of the CTMR when faced with stressful events such as visiting the veterinary clinic or having a stranger enter their home and perform examinations.

Interestingly, in the 52 cats whose owners were requested to perform the CTMR by themselves at home, the normal response rate was 100%. Only 33 (63%) of these cats showed a normal CTMR response when examined by the author initially. This result may further affirm our postulation that stress, rather than the examination technique, strongly influences the CTMR performance in cats. The CTMR is not the only neurological test described to be influenced by stress. Taylor and Kerwin ⁷ stated that cats might display false-negative examination results when frightened or stressed. The menace response, physiologic nystagmus, pupillary light reflex and knuckling postural reaction may be difficult to perform or yield abnormal results. Quitt et al ⁸ evaluated the menace response using three methods in 50 healthy cats. The menace response could always be elicited with at least one technique, but the positive response rate was in the range of 60–84.5% with different techniques. The authors postulated that the animals might be anxious or stressed in unfamiliar environments; hence, they did not perform adequately to such menace stimulation. Theoretically, in contrast to learned responses, reflexes do not involve the sympathetic pathway, hence should not be affected by the cat’s agitation. However, some tendon reflexes have also been described as challenging to elicit. The patellar reflex may appear depressed or absent in a tense animal with extended limbs, which could be the scenario a nervous animal encounters in the hospital. ⁹ Potentially, the altered muscle tone due to stress may have affected the CTMR performance in some of the cats in the current study.

Some individuals responded only to one of the three methods. We suggest that clinicians try different methods to elicit the CTMR if the commonly used method, ‘pinch skin with haemostat forceps’, does not yield a positive response. It is possible that the displacement of fur better resembles the stimuli that cats may encounter in their natural habitat, such as insects landing on the hair coat. This may indicate that to successfully stimulate CTMR in cats, a more lightweight or subtle stimulus is preferred. However, this study did not measure the pressure or strength of the stimuli given when pinching, displacing or poking; hence, this assumption remains unelucidated. The present study showed that some healthy feline subjects might display asymmetrical results or abnormal cranial CTMR cutoff, especially with method C. Although the exact reason remains uncertain, variable stimuli generated via a small contact surface, such as the tip of a paper clip, was postulated.

In the present study, the CTMR could not be elicited normally with any method in 40% of cats when examined by the author. Together with the variable response, the CTMR might not be the best test to aid lesion localisation for cats in the clinical setting, even when interpreted with the rest of the neurological examination. If the CTMR result is crucial for a specific patient, the clinician teaching the owner how to perform the CTMR at home and interpreting a video provided by the owner may be an option. However, most cat owners enrolled in this study were staff or students from NTUVH. Although not specially trained in the neurological field, they are likely to have a better understanding of cat anatomy and could have learned the CTMR more easily. In addition, the CTMR results were reported verbally by the owner in the present study, and no video was recorded for the authors to confirm the results objectively. Further study is warranted to evaluate the feasibility of ‘naive’ owners (non-veterinary professionals) performing the CTMR at home and the accuracy of clinicians interpreting the CTMR from the video provided by the owner.

Several limitations were present in the study. The results of CTMR influenced by stress is merely postulated. Despite the acclimatisation period prior to manipulation and the company of owners throughout the examination, many cats became increasingly anxious and attempted to escape. In addition, aggression was recorded in 31% of cats, indicating a stressed situation. However, stress-related physical parameters (such as heart rate and blood pressure) were not recorded; hence, there is no objective evidence demonstrating the degree of stress in these cats. Intra- and inter-observer agreement was not assessed in the present study. The CTMR reflexes were performed by only one examiner (CYT) who had 2–3 years of clinical experience in small animal neurology; therefore, the intra-observer variability was postulated to be minimal. Future studies are needed to evaluate the influence of the examiner’s experience. Another limitation is the lack of randomisation in the order of the three methods. The CTMR results were only reported verbally by the owner and no video was available for further confirmation, which should also be considered a limitation.

Conclusions

When performed by a clinician after a full neurological examination, the overall normal response rate of the CTMR in healthy cats in Taiwan was low. The method ‘displace fur with the tip of a pen or haemostat forceps’ yielded the highest normal response rate. However, approximately half of the cats displayed abnormal results using this method. Regardless of the location of the examination, the CTMR results obtained by clinicians may not reflect the actual function. Based on our results, the CTMR might not be a suitable test to aid lesion localisation for cats in a veterinary clinic.