This study was a cross-sectional study conducted at the Army Hospital (Research and Referral) in New Delhi, India during the period from October 2019 to April 2021. Ethical clearance was obtained from the hospital’s ethical clearance committee (IEC No: 74/2019). Patients of any ethnicity or age from across the country who were referred to or brought to this hospital were enrolled. The patients came from both rural and urban backgrounds. Those who agreed to participate in the study provided signed written informed consent and satisfied the following inclusion criteria.

Inclusion criteria: Patients with a confirmed diagnosis of diabetes, with or without ulcers (early stages of Wagner classification [2] in the foot), at the Department of General Surgery of a tertiary care hospital were included in the study.

Exclusion criteria: Patients with diabetic foot selected for amputation and further flap coverage were excluded from the study, as these individuals would not be able to undergo testing for TTS after amputation. Patients with vascular insufficiency (Ankle-Brachial Pressure Index [ABPI] <0.7) were also excluded, as ischaemic pain due to vascular insufficiency would hinder the diagnosis of TTS. Patients in severe sepsis or those who were unstable were excluded from the study, as they would not be able to undergo testing for TTS. Additionally, patients with later stages of Wagner ulcers, as those would typically require amputation were excluded from the study.

Thirty consecutive diabetic patients presenting with pain, burning, numbness, and paraesthesia of the heel or feet, with or without ulcers, were evaluated. All patients were tested for fasting and postprandial blood sugar levels and HbA1c. Clinically, all patients were evaluated through a three-point sensory testing using Semmes-Weinstein 10 g filaments (measured on a scale of 0 to 10 at a minimum of four sites: heel, toe, lateral malleolus, and medial malleolus), Tinel’s sign at the tarsal tunnel, and the presence of ulcers on the foot. All patients underwent Nerve Conduction Velocity (NCV) studies performed by a neurologist at this hospital, which included assessments of distal motor and sensory latency and Sensory Nerve Action Potential (SNAP). Imaging studies in the form of MRI were conducted for a complete work-up of these patients and further diagnosis of TTS.

All demographic data, clinical examination results, nerve conduction study results, and MRI findings were recorded in an MS Excel spreadsheet. The data were coded and analysed using Statistical Package for Social Sciences (SPSS) version 23.0 (IBM Corp). Descriptive statistics were generated using means/standard deviations and medians/Interquartile Ranges (IQRs) for continuous variables, and frequencies and percentages for categorical variables. Group comparisons were performed using the Chi-square test. Sensitivity of the test was calculated by dividing the number of true positives by the sum of true positives and false negatives. Specificity of the test was calculated by dividing the number of true negatives by the sum of true negatives and false positives. Statistical significance was set at a p-value of 0.05.

The mean age of presentation was 61.4±11.2 years, and the median age was 59 years. Of the 30 patients enrolled, 20 were males (66.7%) and 10 were females (33.3%) [Table/Fig-1].

The mean fasting blood sugar and postprandial levels were 163.7±78 mg/dL and 228.5±84.3 mg/dL, respectively. The mean HbA1c level was 8.5±1.04% [Table/Fig-2]. The incidence of TTS in diabetic patients was found to be 14 (46.7%) electrodiagnostically, 22 (73.3%) clinically, and 25 (83.3%) radiologically.

The most common finding in the imaging conducted was oedema, which was observed in 25 (83.3%) patients. Inflammation and ganglion cysts were seen in 4 (13.3%) and 3 (10%) patients, respectively [Table/Fig-3].

[Table/Fig-3]:

MRI findings of the patients.

Tinel’s sign was positive in 22 (73.3%) of patients. Additionally, 10 (33.3%) of patients exhibited a loss of sensation when measured on a scale of 10 at a minimum of four sites (heel, toe, lateral malleolus, and medial malleolus). Non healing diabetic ulcers were present in 17 (56.7%) of patients [Table/Fig-4].

[Table/Fig-4]:

Findings of clinical evaluation of patients.

On electrodiagnostic studies, the motor amplitude was not recordable in 10 (33.3%) of patients. The H reflex was not recordable in 21 (70%) of patients, and the sensory amplitude was not recordable in 26 (86.7%) of patients [Table/Fig-5].

The positivity of Tinel’s sign was significantly associated with electrodiagnostic confirmation of TTS (p-value=0.0001). The monofilament test was also significantly associated with electrodiagnostic confirmation of TTS (p-value=0.039) [Table/Fig-6].

Clinical findings were confirmed by electrodiagnostic findings in 17 (56.7%) of patients. Radiological confirmation of TTS was corroborated by electrodiagnostic studies in 15 (50%) of patients. The clinical findings of TTS were confirmed by radiological findings in 80% of patients [Table/Fig-7].

The sensitivity of the association between clinical findings and electrodiagnostic studies was 78.57%, with a specificity of 62.5%. The sensitivity of the association between radiological findings and electrodiagnostic studies was 92.86%, with a specificity of 87.5%. The sensitivity of the association between clinical findings and radiological studies was 87.5%, with a specificity of 50% [Table/Fig-8].

In this study, the mean age of presentation was 61.4±11.2 years, with a male predominance (66.7%). A similar study by Rinkel WD et al., which examined 113 patients in the Netherlands, reported a comparable mean age of 62.7 years [10].

Examination also included Tinel’s sign, which involves light tapping over the nerve to elicit a sensation of tingling or “pins and needles” along the distribution of the nerve. It is considered positive when the tingling or prickling sensation is felt. This sign was found to be positive in 73.3% of patients, with a significant p-value of 0.0001. Cimino WR found this in all 97 patients in their review of the literature [11]. Linscheid RL et al., found that Tinel’s sign was positive in 24 out of 34 patients in their study conducted in Atlanta [12].

MRI findings suggestive of oedema were the main reason for compression of the common peroneal nerve and tibial nerve in the tarsal tunnel. Oedema was the predominant finding present in 25 patients (83.3%). Jung HJ et al., conducted a study on 33 patients in Incheon, Korea, and suggested that MRI is excellent for demonstrating musculotendinous and neurovascular structures [8]. MRI can clearly reveal the anatomy of the tarsal tunnel and its contents, along with the presence or extent of space-occupying lesions leading to TTS [13]. Kerr R and Frey C found that oedema was the main factor associated with inflammation of the tibialis posterior tendon within the tunnel [14].

Sensory nerve conduction studies were more sensitive and yielded more convincing diagnostic findings. Approximately 26 patients (86.7%) had no recordable potentials, while four patients (13.3%) had normal findings. Patel AT et al., found that SNAP were absent in 92.8% of patients with TTS, while mixed nerve conduction studies were abnormal in 85.7% of patients [15]. Sodani A et al., conducted a study on 40 patients in India and found that motor nerve conduction studies were significantly abnormal in patients with TTS [16]. These findings are quite comparable to those of present study.

This was a single-centre study. All three modalities for diagnosing TTS-clinical, radiological, and electrodiagnostic studies-were used in this study. Longer follow-up durations and further studies are needed to ascertain the impact of these factors on long-term complications in type II diabetic patients.

The study had a small sample size. Patients with diabetic foot at risk who had a low Wagner’s grade were included in the study, while those with a higher Wagner’s grade were excluded.

The diagnosis of TTS can be challenging. It is primarily based on clinical examinations such as the monofilament test, Tinel’s sign, and the assessment of diabetic ulcers. To further support the diagnosis, imaging modalities like MRI can be useful for evaluating the depth of the tunnel and the status of the underlying structures, including oedema, inflammation, and compression due to synovial fluid effusion or ganglia. Additionally, electrodiagnostic studies can help confirm the diagnosis.