Therapy-Disability-Neurology Grade (TDN Grade)

About the TDN grading

The Therapy-Disability-Neurology (TDN) grading system is a novel multidimensional classification of complications severity.

Whilst other classifications of adverse events (AE) in neurosurgery define severity according to the therapy, this new grading system accounts for therapy, disability and neurological deficits, as listed below:

Dimension 1: Therapy (T1 to T5)

Where adverse event is: 

• T1 = not requiring any treatment other than antiemetics, antipyretics, analgesics, diuretics, electrolytes, bedside opening of wound infections (corresponds to CDG = 1 and LIC = Ia);
• T2 = requiring pharmacological treatment, blood transfusion or total parenteral nutrition (corresponds to CDG = 2 and LIC = 2a);
• T3 = requiring surgical, endoscopic, or radiological intervention (corresponds to CDG = 3 and LIC = 2);
• T4 = life-threatening and requiring management in intensive care (corresponds to CDG = 4 and LIC = 3);
• T5 = resulting in death (automatically TDN Grade = 5, T5D5N2; corresponds to CDG = 5 and LIC = 4).

Dimension 2: Disability (D1 to D5)

Where the adverse event is:

• D1 = not hindering at daily life activity (corresponds to mRS = 1);
• D2 = hindering at least one activity of daily living (corresponds to mRS = 2 to 3);
• D3 = hindering walking, preventing the patient from attending his own bodily needs (corresponds to mRS = 4);
• D4 = leaving the patient bedridden, in need of constant help, incontinent (corresponds to mRS = 5);
• D5 = resulting in death (automatically TDN 5, T5D5N2; corresponds to mRS = 6).

Dimension 3: Neurology (N1 to N2)

Where the adverse event is:

• N1 = not resulting in any new neurologic deficit;
• N2 = resulting in at least one new neurologic deficit.

The definition of the Therapy-Disability-Neurology (TDN) grades is based on three dimensions. The therapy, based on the Clavien-Dindo-Grading system (CDG) and the Landriel Ibañez Classification (LIC), the disability, using the modified Rankin Scale (mRS), and the neurology, using a binary definition.

The output of the grading system is first the TDN grade (the highest dimension chosen) and then each dimension separate. It is important to note that the dimensions of disability and neurology should only be considered when these have deteriorated since the preoperative state. This impairment must result from the adverse event.

© Terrapon APR

The TDN grading is aimed at facilitating adverse effects severity classification throughout medical facilities and was found to be consistent with the clinical and economic repercussions of AEs in neurosurgery.

Published in 2021, the original study by Terrapon A. et al. consists of a two-center retrospective observational study on 6071 interventions covering the whole neurosurgical spectrum.

Within the first patient cohort (4680 interventions) a positive correlation was found between AE severity and length of hospital stay (LOS) and cost of medical care, as well as the results on the Karnofsky Performance Status Scale (KPS) at discharge and at follow-up.

Same corelations between AE severity and LOS and KPS were more pronounced in the external validation cohort (the remaining 1391 interventions).

References

Original reference

Terrapon APR, Zattra CM, Voglis S, Velz J, Vasella F, Akeret K, Held U, Schiavolin S, Bozinov O, Ferroli P, Broggi M, Sarnthein J, Regli L, Neidert MC. Adverse Events in Neurosurgery: The Novel Therapy-Disability-Neurology Grade. Neurosurgery. 2021 Jul 15;89(2):236-245. doi: 10.1093/neuros/nyab121. PMID: 33887774.

Other references

1. Gómez Vecchio T, Corell A, Buvarp D, Rydén I, Smits A, Jakola AS. Classification of Adverse Events Following Surgery in Patients With Diffuse Lower-Grade Gliomas. Front Oncol. 2021 Dec 21;11:792878. doi: 10.3389/fonc.2021.792878. PMID: 34993147; PMCID: PMC8724913.

2. Millward CP, Doherty JA, Mustafa MA, Humphries TJ, Islim AI, Richardson GE, Clynch AL, Gillespie CS, Keshwara SM, Kolamunnage-Dona R, Brodbelt AR, Jenkinson MD, Duncan C, Sinha A, McMahon CJ. Cranioplasty with hydroxyapatite or acrylic is associated with a reduced risk of all-cause and infection-associated explantation. Br J Neurosurg. 2022 Jun;36(3):385-393. doi: 10.1080/02688697.2022.2077311. Epub 2022 May 24. PMID: 35608052.

3. The therapy dimension is based on the CDG: Dindo D, Demartines N, Clavien PA. Classification of surgical complications: a new proposal with evaluation in a cohort of 6336 patients and results of a survey. Ann Surg. 2004 Aug;240(2):205-13. doi: 10.1097/01.sla.0000133083.54934.ae. PMID: 15273542; PMCID: PMC1360123.

4. The Disability dimension is based on the mRS: Farrell B, Godwin J, Richards S, Warlow C. The United Kingdom transient ischaemic attack (UK-TIA) aspirin trial: final results. J Neurol Neurosurg Psychiatry. 1991 Dec;54(12):1044-54. doi: 10.1136/jnnp.54.12.1044. PMID: 1783914; PMCID: PMC1014676.