Is it time for a guideline on the use of immunohistochemistry in forensic pathology?

In the field of forensic trauma pathology, immunohistochemistry (IHC) and specialized staining techniques are crucial to estimate the age of the wound and to identify complications stemming from the trauma. In addition, they are essential to detect unique cases, including those of asphyxia and severe head trauma (Chen et al. 2021).

The use of IHC is also promising for tackling fundamental questions in forensic medicine, such as those related to the age-dating of skin injuries, surpassing the limitations of older techniques based on histochemical techniques (Tomassini et al. 2022; Tomassini et al. 2024).

Despite its promise, the rate of IHC staining undergoes significant variations over time after death, due to postmortem involutional phenomena affecting tissues and altering their antigen-antibody affinity. This has been demonstrated by studies conducted on populations consisting of medico-legal autopsies (Lesnikova et al. 2018).

This is indeed critical, as the practical application of IHC is documented in the literature and proposed in a variety of very complex and sensitive procedural contexts. For example, in homicide cases, where a positive immunohistochemistry result can provide substantial evidence to establish trial truth (Tong et al 2017).

Hence, the use of IHC in forensic pathology is an extremely sensitive issue, as the literature in this field has advocated the application of these techniques in a vast variety of cases related to both natural and violent deaths.

Often, these recommendations are based on studies conducted on relatively small cadaveric populations and not always through adequate standardization of the study population. This is surprising considering that, in courts of law, forensic pathologist consultants frequently invoke the negativity or positivity of a particular IHC staining; this raises the question—assuming the character of evidence before a court -: is that technique truly scientifically validated? Are there clear indications from guidelines and/or protocols regarding the use of one technique over another, or under what conditions the use of either technique should be excluded?

At this juncture, there is a compelling need for the issuance of clear guidance indicating when these techniques may be employed and under what conditions. Specifically addressing the time since death within which the technique is valid, its state of preservation, and the susceptibility of the IHC technique to post-mortem modifications. This is necessary to ensure the proper utilization of these techniques and to provide a fruitful incentive for their study and further exploration in various forensic-medical issues that remain largely unresolved.