The musculoskeletal phenotype of fatal strychnine poisoning

Abstract Background Strychnine poisoning is still a documented entity in forensic medicine. Strychnine is a competitor of the post-synaptic glycine receptors at the level of motor neurons and interneurons in the spinal cord, which blocks glycine inhibitory effects on post-synaptic neurons leading to involuntary muscle contractions. Strychnine poisoning appears with an initial excitability, followed by vomiting, development of convulsions, with muscle contractions, and can result fatal due to spasm of respiratory muscles. Although it is widely accepted that diaphragm and accessory respiratory muscles are primarily responsible of death, the impact of strychnine at the level of skeletal muscle fibers morphology has been poorly investigated, and the literature does not report evidence to understand the precise effect of strychnine on skeletal muscles cytological organization. Indeed, the study of the effects of strychnine and other poisons is challenging because of the heterogeneity of skeletal muscle fibers and their distinct physiological properties, which could determine different responses to each toxic substance. Case presentation We report a suicidal case of a 50-year-old man who died following the ingestion of a lethal dose of strychnine. At the time of the crime scene examination, rigor mortis was present and fully established. A complete post mortem examination was performed few days after death. By the time the body was examined on the autopsy table, rigor mortis had already resolved. This was consistent with the expected evolution of rigor mortis over the interval between the crime scene examination and the autopsy. The autopsy examination revealed enlargement of both lungs with abundant blood-tinged fluid and foam on the main bronchi. From toxicological analyses, it emerged that massive concentrations of strychnine were present in peripheral blood, gastric contents and vitreous humor. To comprehend the impact of strychnine poisoning to respiratory muscles we performed a morphological and immunofluorescence characterization of the diaphragm and pectoralis major muscles. Conclusions Our observations suggest that strychnine poisoning profoundly impacts the morphology of diaphragm fibers, with both fast and slow fibers presenting hypercontraction areas. While the accessory respiratory muscle pectoralis major presents milder alterations, with fewer fibers with hypercontraction areas. This work represents the first histological investigation on the impact of strychnine on skeletal muscle fibers, and suggests distinct influence of this poison on diaphragm and pectoralis major muscles.