Four weeks of having hot flushes made me wonder if I was getting my menopause 20 years too early. Or whether it could be related to medications. An even more plausible explanation could be that our internal temperature gauge may be functioning improperly with HNPP. So how sensitive are our bodies to hot and cold?
Peripheral nerves connect the brain and spinal cord to muscles and to sensory cells that detect sensations such as touch, pain, heat, and sound. Damage to the peripheral nerves can result in loss of sensation as well as wasting (atrophy) of muscles in the feet, legs, and hands.
In spite of this, the control of body temperature takes place in the central nervous system at different levels, from the spinal cord to the upper parts of the brain. According to the 1996 report The Autonomic Nervous System and Body Temperature by R. H. Johnson, the maintenance of body temperature depends upon a balance between heat loss and heat production. The mechanisms by which heat loss and production are regulated are very similar; each may be regulated in two ways:
- By reflexes from peripheral temperature receptors in the skin: the reflex pathway probably passes through the brain and its activity may be determined by the level of central temperature.
- By means of receptors within the brain which respond to changes in blood temperature. 
However, instead of feeling the extremes of hot and cold due to autonomic neuropathy, studies suggest that we’re more likely to feel nothing at all. HNPP’ers on the other hand have spoken about becoming particularly sensitive to the weather.
“It’s been cold this week, I’m now sporting three pairs of socks and my feet still feel cold! I don’t think it’s to do with circulation, more misfiring nerve-endings, which just scream ‘cold’. The odd thing is though is that I’ve been getting burning sensations in my feet… burning cold.”
From Jon Leonard’s blog – My Life with HNPP
The idea of loss of sensation can be seen in PMP22 Mutation Causes Partial Loss of Function and HNPP-like Neuropathy. Both a 35-year-old man and woman complained of a “decrease in pain and temperature sensation”. The authors say in these cases “heterozygous T118M mutations mildly disrupt myelin to an extent that mild symptoms are likely to develop; homozygous mutations more severely disrupt peripheral nerve and disable patients”. But this appears only in this kind of specific mutation.
According to the 1997 study Hereditary Thermosensitive Neuropathy: An Autosomal Dominant Disorder of the Peripheral Nervous System, both Charcot Marie-Tooth disorder and HNPP had no links to this condition. HTN is also autosomal and inherited, with patients suffering from body temperatures of over 38.5 C.
The reason the authors give for it being unrelated was: “We excluded loci causing other hereditary demyelinating neuropathies, such as Charcot-Marie-Tooth disease type I (CMT type I) and hereditary neuropathy with liability to pressure palsies (HNPP), by linkage analysis; thus, HTN is not allelic to either CMT type I or to HNPP.”
This is reiterated in the book Peripheral Neuropathy in Childhood in which the authors Robert A. Ouvrier, J. G. Mcleod, and J. D. Pollard mention the above study adding that Hereditary sensory and motor neuropathy (HSMN) was also excluded from the research. That being said, there is very little research into this condition, with many journals relying simply on the 1997 report.
Why temperature is seen to be connected
Interestingly, the report by R. H. Johnson as mentioned above, does put a small disclaimer about body temperature being controlled by the central nervous system, saying: “Strictly speaking heat production by shivering is mediated by motor nerves but is included so that temperature regulation may be kept in proportion.”
He goes on to say that there is a combination of peripheral nerve issues as well as the central nervous system that causes problems with temperature: “The abnormalities of temperature regulation occur with failure of peripheral effector structures, alteration of function of central controlling structures or with lesions of interconnecting nerves.”
Why temperature in HNPP is seen to unrelated
This can be seen in several studies including Thermoregulation in Peripheral Nerve Injury-Induced Cold-Intolerant Rats. In 2012, scientists from the University Medical Centre Rotterdam, Netherlands, tested cold temperatures on rats that had peripheral nerve injuries. By attempting to re-warm the paws of the animals over three to nine weeks, the researchers concluded that “re-warming patterns are not altered after peripheral nerve injury in these rat models despite the fact that these animals did develop cold intolerance”.
They go on to add: “This suggests that disturbed thermoregulation may not be the prime mechanism for cold intolerance and that, other, most likely, neurological mechanisms may play a more important role.
“There is no direct correlation between cold intolerance and re-warming patterns in different peripheral nerve injury rat models.”
Peripheral nerves and thermoregulation
It’s obvious that the peripheral nerve system does play a part in feeling the differences between temperatures. In an 2009 study, nerve conduction tests were carried out on 45 Indian women between the ages of 18-25. The researchers say: “Patients with impaired circulation may have a reduced tissue temperature and additional reduction of nerve conduction velocity.” Information carried from peripheral temperature sensors tends to effect the temperature of the skin.
Authors of the 1985 research Skin-Temperature Stability between Sides of the Body reinforce this notion saying: “In normal persons, the skin temperature difference between sides of the body was only 0.24 degree +/- 0.073 degree C. In contrast, in patients with peripheral nerve injury, the temperature of the skin innervated by the damaged nerve deviated an average of 1.55 degrees C.”
It’s evident that the central nervous system, and more importantly key brain centres are mainly concerned with temperature control as well as the preoptic area and anterior hypothalamus – a portion of the brain that contains a number of small nuclei with a variety of functions.
However, scientists at the Max Delbrück Center for Molecular Medicine in Berlin, Germany, states that these hypothalamic regions harbour neurons not only detect changes in core body temperature, but are also believed to “receive and integrate input from ascending somatosensory pathways carrying information from peripheral temperature sensors”.
Despite those with HNPP clearly suffering from problems with temperature regulation, unless the connection between the autonomic nervous system is more distinctly laid out, research in this area will continually be put on the back burner. Nonetheless, there are reasons behind why we may feel cold during particularly bad weather so you’re not the only one.
- 1. “The Autonomic Nervous System and Body Temperature” – R. H. Johnson, 1966