'Functional hyperthermia': a historical overview

Disabling symptoms associated with increased axillary temperature in patients with functional hyperthermia

BACKGROUND

I previously reported a case of functional hyperthermia (FH) in a patient with an axillary temperature just slightly above 37.0 °C who persistently requested treatment. Because the severity of her fatigue increased remarkably when her axillary temperature increased above 37.0 °C, she felt that the temperature of 37.0 °C was disabling. In the present study, I analyzed a larger number of patients with FH to investigate the incidence of disabling symptoms with increasing body temperature, the kinds of symptoms associated with increased body temperature, and the temperatures at which these symptoms became disabling.

MAIN BODY

Twenty patients with FH (7 men, 13 women; mean age ± standard deviation, 31.2 ± 10.9 years) who visited my department were asked whether they had any disabling symptoms associated with an increase in axillary temperature and, if so, at what temperature the symptoms became disabling. Sixteen of 20 patients (80.0%) responded that they had such symptoms, which included worsening of general fatigue (n = 12, 75.0%), feelings that their brain did not work properly (n = 5, 31.3%), inability to move (n = 4, 25.0%), hot flashes/feeling of heat (n = 3, 18.8%), headache (n = 2, 12.5%), dizziness (n = 2, 12.5%) and anorexia (n = 1, 6.3%). The axillary temperatures at which patients felt worsening fatigue ranged from 37.0 °C to 37.4 °C in 7 of the 12 patients (58.3%) who experienced worsening fatigue. The patients also reported that the disabling symptoms, with the exception of headache, were not alleviated by antipyretics.

CONCLUSIONS

Many patients with FH reported worsening fatigue as a disabling symptom associated with increased axillary temperature; more than half of those patients experienced worsening fatigue in the temperature range of 37.0 °C to 37.4 °C. These findings suggest that the reasons patients with FH consider 37 °C disabling and seek medical treatment are that physical symptoms such as fatigue worsen at 37 °C, although this temperature is assumed by many physicians to be within the normal range or just above the normal range of axillary temperature, and that most hyperthermia-associated symptoms are not alleviated by antipyretic drugs.

Characteristics of Functional Hyperthermia Detected in an Outpatient Clinic for Fever of Unknown Origin

Background: Functional hyperthermia (FH) is characterized by hyperthermia resulting from sympathetic hyperactivity rather than inflammation, and it is frequently overlooked by medical practitioners due to the absence of abnormalities in a medical examination. Although FH is an important differential diagnosis for fever of unknown origin (FUO), the literature on FUO cases in Japan lacks information on FH. In this study, we aimed to uncover the population of FH patients hidden in FUO cases. Methods: An outpatient clinic for FUO was established at Okayama University Hospital, and 132 patients were examined during the period from May 2019 to February 2022. Results: A diagnosis of FH was made in 31.1% of the FUO cases, and FH predominantly affected individuals in their third and fourth decades of life with a higher incidence in females (68.3%). The frequency of a history of psychiatric illness was higher in patients with FH than in patients with other febrile illnesses. Although the C-reactive protein (CRP) is generally negative in FH cases, some obese patients, with a body mass index ≥ 25 had slightly elevated levels of CRP but were diagnosed with FH. Conclusions: The results showed the importance of identifying FH when encountering patients with FUO without any organic etiology.