By Marcello Cherchi, MD PhD
For patients
Jet propulsion type 8 (JP-8) is used as fuel for military jets, ground vehicles and other purposes. Human and animal studies suggest that it can cause hearing and balance problems. If your doctor suspects this, then they may check several tests of hearing and balance function. If it seems that these symptoms are due to JP-8 exposure, then the exposure should be stopped.
For clinicians
Overview
Jet propulsion type 8 (JP-8) is used for multiple military purposes, including as fuel for jet planes, ground vehicles, generators, illuminators, HVAC systems and cooking stoves. JP-8 is a kerosene-based fuel consisting of several hundred aromatic and aliphatic hydrocarbons. JP-8 can enter the circulation via inhalation or through the skin. Animal studies show that JP-8 exposure can interfere with auditory function. Small human case series of patients exposed to JP-8 for 3 – 5 years show that JP-8 exposure is associated with bilateral vestibular weakness, which is detectable on rotatory chair testing (RCT). There are some serum and urinary biomarkers of JP-8 exposure. Treatment is cessation of exposure, though human case series report that symptoms can persist for years.
Introduction
Jet propulsion type 8 (JP-8) fuel is used for miliary aviation in the United States Air Force and in NATO, as well as some military ground vehicles, generators, illuminators, HVAC systems and cooking stoves.
Epidemiology
Given its broad uses, many military personnel have probably been exposed (Merchant-Borna et al. 2012; Pleil et al. 2000). In contrast, commercial airliners use Jet A and Jet A-1 fuels (Adekitan et al. 2018; Ritchie et al. 2003).
Pathophysiological mechanism of disease
JP-8 is a kerosene-based fuel consisting of several hundred aromatic and aliphatic hydrocarbons (Fife et al. 2018). Hydrocarbon exposure in general has been reported to cause cognitive and vestibular dysfunction (Hodgson et al. 1989), and specifically JP-8 is similar (Proctor et al. 2011; Tu et al. 2004). The exact mechanism by which specifically JP-8 causes symptoms remains unclear, though animal studies suggest that it induces apoptosis (Stoica et al. 2001).
JP-8 can be inhaled or absorbed through the skin (Kim et al. 2006; McDougal et al. 2000).
Animal studies (rats) show that JP-8 increases vulnerability to noise-related hearing loss (Fechter et al. 2012; Fechter et al. 2007), decreases neural transmission (Guthrie et al. 2015), interferes with the encoding of stimulus intensity (Guthrie et al. 2014) and can cause abnormal otoacoustic emissions (Fechter et al. 2010).
Fife and colleagues (Fife et al. 2018) reported on a series of 3 patients exposed to JP-8 who developed bilateral vestibular weakness as measured on rotatory chair testing (RCT). It is unclear whether this deficit is the result of peripheral vestibular dysfunction, or central vestibular dysfunction, or both.
Clinical presentation
Fife and colleagues (Fife et al. 2018) reported on a series of 3 patients who had been exposed to JP-8 for 3 – 5 years. The patients said that the symptom of imbalance developed gradually over “2 years” (in one patient) to “several years” (in two patients), and tended to be intermittent. None of the patients complained of hearing loss or tinnitus, but endorsed a variety of non-audiovestibular complaints (headache, fatigue, blurry vision, eye/skin irritation, coughing, sinus congestion, chest tightness, palpitations, numbness, irritability, depression).
Physical examination
In the series of three patients reported by Fife and colleagues (Fife et al. 2018), one patient had difficulty with Romberg stance, one patient had difficulty with tandem gait, and one patient’s examination was normal.
Ocular motor examination
In the series of three patients reported by Fife and colleagues (Fife et al. 2018), none had detectable ocular motor findings on face-to-face examination.
Testing: vestibular
In the series of three patients reported by Fife and colleagues (Fife et al. 2018), all three exhibited low gain on slow harmonic acceleration; in two patients this was across all frequencies (0.01 – 0.64 Hz), and in one patient it was in middle frequencies (0.04 – 0.16 Hz). The first two patients exhibited bilaterally reduced caloric responses; the third patient exhibited a 33% left-sided weakness.
Studies of persons exposed to JP-8 reach different conclusions regarding computerized dynamic posturography (CDP), with some studies detecting abnormalities (Smith et al. 1997) and others not (Maule et al. 2013).
Testing: other
Biomarkers for JP-8 exposure include several compounds detectable in the blood (Maule et al. 2016) and urine (Serdar et al. 2003; Smith et al. 2012).
In the series of three patients reported by Fife and colleagues (Fife et al. 2018), two patients underwent electroencephalography (EEG), which was normal.
Imaging
In the series of three patients reported by Fife and colleagues (Fife et al. 2018), two patients underwent brain MRI, which was normal.
Differential diagnosis
The differential diagnosis is that of other diseases that can manifest with bilateral vestibular weakness (BVW).
Treatment
There is no known treatment for JP-8 toxicity, but the exposure to JP-8 should be stopped. A trial of vestibular rehabilitation therapy (VRT) is logical (given its application in other forms of vestibular weakness), though has not been studied specifically for patients with JP-8 exposure.
Prognosis
In the series of three patients reported by Fife and colleagues (Fife et al. 2018), one patient followed up after 16 years and reported that her “dizziness is mild” but still present. In one patient, caloric responses improved at 16 months after exposure to JP-8 was stopped.
References
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