In the current study, by using DTI hypothalamic injuries were investigated in patients exhibiting hyperhidrosis following mild TBI. Our results are summarized as follows: 1) the patient group had lower FA values and higher ADC values for both sides of the hypothalamus than those of the control group (p < 0.05); and 2) all patients exhibited a HDSS score of two or greater. The FA and ADC values are commonly used to demonstrate the status of brain structures in patients with brain injuries. The FA value indicates the degree of directionality of water diffusion; consequently, it reflects fiber density, axonal diameter, and white matter myelination, whereas the ADC value indicates the magnitude of water diffusion31. Therefore, a low FA value combined with a high ADC value is indicative of brain injury32. In the present study, the FA and ADC values indicate the presence of hypothalamic injuries in the patient group and these injuries might be related to the concurrent presence of hyperhidrosis in the patient group.
Hyperhidrosis is a clinical feature of PSH3,4, and PSH presence is determined, in the absence of other potential causes such as uncontrolled sepsis or airway obstruction, by the transient presence of four of the following six criteria: fever, tachycardia (heart rate >120 beats/min or >100 beats/min if treated with a beta-blocker), hypertension (systolic blood pressure >160 mmHg or pulse pressure >80 mmHg), tachypnea (respiratory rate >30 breaths/min), hyperhidrosis, and extensor posturing or severe dystonia 3,4. Although the pathophysiological mechanisms of PSH have not clearly elucidated, two main mechanisms have been suggested: 1) simple disconnection of cortical inhibitory centers such as the insula and cingulate cortex to the brain areas responsible for supraspinal control of sympathetic tone (hypothalamus, diencephalon, and brainstem); and 2) the excitatory:inhibitory ratio model in which paroxysms are driven by abnormal processing of afferent stimuli within the spinal cord following disconnection of descending inhibitory pathways7,9,12,33. Although no patient in this study satisfied the diagnostic criteria for PSH, we suggest that the hyperhidrosis exhibited by our patients may be considered a clinical feature indicative of PSH because the hypothalamus is an important area for the development of PSH7,12,33. We assume that the reason our patients could not meet the diagnostic criteria of PSH is related to their head injuries being milder than that of moderate and severe TBI.
The hypothalamus has been regarded as a key regulator of thermoregulatory sweating10,11. Several studies have reported associations between hypothalamic injury and hyperhidrosis in patients with brain injury, including those with cerebral infarct and multiple sclerosis15-18. Therefore, the results of our study appear to be consistent with those of the abovementioned studies15-18. To the best of our knowledge, this is the first study to demonstrate an association between hyperhidrosis and hypothalamic injury in patients with mild TBI. However, limitations of this study should be considered. First, the technique for measurement of DTI parameters is operator-dependent, particularly during the definition of the region of interest; regardless, we attempted to define consistently the hypothalamus by using definite boundaries in this study34. Second, a small number of subjects were recruited in this study. Therefore, conduct of further prospective studies that enroll larger numbers of subjects should be encouraged.
In conclusion, by using DTI, we detected hypothalamic injury in patients who showed hyperhidrosis after mild TBI. Based on the results, it appears that hyperhidrosis exhibited by patients with mild TBI can be related to hypothalamic injury. Our results suggest that DTI could be useful in detecting hypothalamic injury, injuries that may not be detected on conventional brain MRI in patients with mild TBI.