Neuropathic pain as consequence of rifle injury: a case report and literature review
Authors: Guimarães Mário Vicente Campos , Martins Josué Andrade , Oliveira Ana Lívia Piovezan de , Cardoso Cecília Procópio 
Published: July 2023

Rifle injuries are relatively common in emergency cases. It may result in several acute damages or it could lead to chronic consequences to the patient. This paper reports a case of a rifle injury on the leg that resulted in neuropathic pain and venous insufficiency. To treat this patient, a multidimensional approach was prefered, using comprehensive therapy, drug treatment and neuromodulation. The case reported in this paper was gathered by appreciation of the patient’s records and interviews and was discussed in the light of the most recent literature. Neuropathic pain is caused by lesion or disease of the somatosensory nervous system, according to The International Association for Study of Pain that affects over 7 to 8 percent of general populations and corresponds to 20 to 25 percent of chronic pain, most frequently in women and man older than 50-years, diagnosed exclusively via clinical criteria. It might be classified by the clinical manifestations: spontaneous pain, evoked pain, after sensations, hyperpathia and referred pain. The details of pathophysiology of neuropathic pain are yet to be clarified once most of the data in the matter comes from animal testing and should be interpreted carefully, majorly in the long-term assessments. It is clear, though, that several mechanisms are involved in the pathogenic process, depending on anatomical location and etiology, and that different classifications of neuropathic pain could be clustered to form several subgroups based on the symptoms combination, each reflecting different mechanisms. Understanding these underlying mechanisms is crucial to a proper treatment of the patient. In this paper, we report a patient who suffered from a fire gun injury in the left feet resulting in a neuropathic pain. A 40-year-old male comes to the office referring to allodynia, hyperalgesia, burning pain and paroxysmal pain, characterizing persistent neuropathic pain, intensity 8 in the one-to-ten scale, and edema during the day in the left inferior member. The patient reports being shot, one year and half before, with a 5.56 caliber rifle at the left feet, riching the fifth metatarsal No remarkable finding was present in the medical history prior to the incident. At physical examination, it was perceived that the patient developed venous insufficiency, for which was prescribed a ⅞ compression socks (30- 40 mmhg). The neuropathic pain was firstly treated with pregabalin 50 mg/ day and Duloxetine 30 mg/day, showing relevant response. Then, electroneuromyography revealed intermedial dorsal cutaneous nerve injury, being managed with a local block, prepared with 8 ml of 2% Lidocaine and 2 ml of 4 mg Dexamethasone, and a 30 Hz neuromodulation, terminating the pain. Ballistic knowledge is essential to a proper management of gunshots injury. In this case report, the patient suffered a 5.56 caliber rifle injury, a high-velocity gun, resulting in an intermediate dorsal cutaneous nerve and the fifth metatarsal lesion. In these injuries, the projectile transfers energy to the affected tissue, expanding and crushing it. This brief expansion creates a subatmospheric pressure resulting in bacterial and foreign material suction into the wound. It is worth to note that gunshot-related injuries in the feet, due to scarce soft tissue, numerous bones and articulations, are more propense to vascular and neural lesions. Although pathophysiological mechanisms of neuropathic pain are not fully understood, it is described post-traumatic peripheral ectopic nerve activity and central sensitization that could help to understand the pain origin. Moreover, coexisting psychological and emotional triggers might be associated with neuropathic pain association. As the electroneuromyography shows, the intermediate dorsal cutaneous nerve, the smallest branch of the fibular nerve, was injured at the fifth metatarsal level rising neuropathic pain. In addition, as mentioned above, gunshot injuries might lead to bacterial invasion, triggering the inflammatory response. In this setting, it is important to point out that evidence suggests inflammatory mediators and proinflammatory cytokines as an inductor factor for pain hypersensitivity. Another possible gunshot related etiology that must be considered is lead toxicity in the composition of gun projectiles, which is reportedly associated with neuropathies. For its heterogeneity of etiologies, mechanisms and presentations, it is essential to understand the underlying causes and its consequences to a proper treatment resulting in partial or full pain relief. In this case, the patient was treated with Duloxetine, a serotonin-norepinephrine reuptake inhibitor and first line to treat neuropathic pain, and pregabalin, an anticonvulsant used to inhibit neuronal excitatory transmission. The synergistic action of these drugs is superior compared to monotherapy. Auxiliary, a local block was performed using Lidocaine analgesic, sodium channel blocker, and Dexamethasone, an antiinflammatory corticosteroid, testifying in favor of mechanical and inflammatory pathogenic mechanism originated by the gunshot injury. Finally, it is worth noting that gunshot wounds might give rise to venous insufficiency as a result of vascular injury and must be carefully considered in order to provide the proper treatment, revascularization for exemple. Another possible cause is deep venous thrombosis and leg injury accounts as a risk factor. In this case, it was opted for compression therapy, a conservative treatment, for increased venous return. Concluding that, neuropathic pain is a heterogeneous condition with a limited action mechanism understanding. It is required from the physicians to comprehend the multiple dimensions and main etiology of this disease in order to provide a proper treatment. As gunshots may contribute to the rise of several damage mechanisms, this case report highlights the importance of acknowledging ballistic properties and possibilities wound-related.