Introduction

Notalgia paresthetica (NP) is described as a chronic neuropathic dysesthesia¹ when you search for it online. This does not seem to be very clear, so let's take a closer look to understand it completely. 

Dysesthesia characterises the sensation that one has with NP, which is an odd feeling of discomfort on the skin. Neuropathic implies that the problem is connected to nerve malfunction or injury. In simpler terms, NP refers to the painful skin sensation that has been present for months or years due to a nerve issue. The upper back, more especially the inside edge of the lower shoulder blade, itches or tingles as a result of the discomfort.

NP can be difficult to diagnose, as it would appear to be a dermal issue at first glance because the symptoms only manifest on the skin (like eczema). However, a closer examination would reveal that it is nerve-related, with the dorsal rami (nerves of the spinal cord) playing a major role in this issue.

This paper will assist in dispelling any confusion regarding why NP is more than simply a skin issue by providing a better understanding of the function of the dorsal rami and the neural pathways that impact it.

Spinal nerves and the nervous system

Let's start by going over the fundamentals of nervous system anatomy. The central nervous system (CNS) and the peripheral nervous system make up the entire nervous system. The brain and spinal cord are the components that comprise the central nervous system (CNS). The dorsal rami are a portion of the peripheral nervous system, which is the network of nerves that connect our body to the brain and spinal cord. 

 The spinal cord, which passes through your spine, serves as a conduit for communication, transmitting motor commands from the brain to your muscles so that you may move and returning sensory data to the brain about pressure, discomfort, or temperature changes experienced by your skin and body. 

The body sends sensory messages, like pain, to the dorsal horns, which are picked up by afferent neurons in the dorsal roots, which carry these impulses and transmit data from the body to the spinal cord. 

The motor neurons that carry messages from the spinal cord to your muscles are located in the ventral horns, which serve an efferent function. Efferent neurons aid in the regulation of reflexes and voluntary motions like picking up a plate. Their axons attach to all of the body's muscles, including those involved in posture and movement.

This two-way road allows you to simultaneously perceive feelings and respond to your environment, which is useful for daily tasks but also essential for situations where you might be in danger. 

Let's take a closer look at the structure of the spinal cord, particularly the areas connected to NP. The core of the spinal cord is made up of the grey commissure, dorsal, ventral, and lateral horns make up the grey matter, which is the core of the spinal cord. The center canal is a narrow channel encircled by the grey commissure. 

There are 31 pairs of spinal nerves that arise from the four main sections of the spinal cord: the cervical, thoracic, lumbar, and sacral.² Your brain and body communicate with each other through these nerves. The thoracic spinal nerves, specifically T2 to T6, are the main focus in the case of NP. These neurons divide into smaller branches known as the dorsal rami after leaving the spinal cord in the upper back. These dorsal rami are in charge of transmitting touch, temperature, and pain signals from the back's muscles and skin to the spinal cord. Small muscles close to the spine receive motor impulses from them as well.

These nerves travel throughout the back in a predictable manner, thus, any compression or irritation brought on by conditions like bad posture, spinal degeneration, or tight muscles might result in the brain receiving inaccurate or misleading signals from the skin. This explains why NP patients experience persistent tingling, burning, or itching in the same area directly beneath the shoulder blade. This nerve, which is frequently connected to these thoracic dorsal rami, is not a skin condition.

The ascending and descending brain pathway

In order to get to the brain, sensory data must first pass through the spinal cord before continuing on an ascending pathway. There are first-order, second-order, and third-order neurons that all play a part in this process. 

After receiving stimuli, first-order neurons send those signals to the spinal cord, where they relay the information to the dorsal horn's second-order neurons. Before it reaches the last group of neurons, the signal gets sent up to the thalamus or cerebellum. From there, it travels to the somatosensory area of the brain, via third-order neurons, where it is processed to allow you to feel and comprehend what is happening to your body.

A descending route from the brain is also present. To instruct your muscles, the brain sends impulses down the spinal cord via descending pathways through efferent neurons. Motor neurons receive these signals and use them to initiate muscle contraction.

The dorsal rami: What are they?

The spinal nerve branches include the dorsal rami, which supply innervation to the neck and back muscles as well as the skin. The medial, lateral, and intermediate branches make up these parts, because the nerves are sent from the CNS to the skeletal muscles; the medial branches are engaged in motor innervation, which enables the contraction and movement of skeletal muscles.^4. These motor innervations transmit sensory information from the skin, joints between the spine bone (called zygapophyseal joints), and the outer layer of bone that surrounds the spine (called the periosteum) to the muscles located deep within the back.⁵ They communicate with the front portion of the neck and trunk, which aids with posture and movement.

Running along both sides of the spine is the longest muscle in the erector spinae group,⁶ the longissimus. The iliocostalis and longissimus muscles receive impulses from intermediate branches. You can bend backwards and stand up straight thanks to these muscles. It gives the sacrospinalis muscle motor and sensory innervations. Additionally, it is a component of the lateral branch that supplies cutaneous sensory innervations to the back's skin.⁷

In addition to its involvement in the intermediate branches, the iliocostalis muscle aids in breathing and the extension and bending of the spine.⁸ It is a component of the lateral branch, which also supplies the back's skin with sensory information. In specific areas, including the L2 and L3 levels on the lower back, this signals the skin over the buttocks.⁹

Your spinal cord gives rise to tiny nerves called dorsal rami. They communicate with the deep muscles in your back, such as the erector spinae, as well as with the skin on your back. When these muscles are tense or irritated, possibly due to bad posture or spinal wear and tear, they can push on the dorsal rami, causing nerve-related symptoms like burning, tingling, or itching in a patch directly beneath your shoulder blade. 

The itching may worsen with stress. Your body's sympathetic nervous system, which activates when you're apprehensive or under pressure, is triggered when you're under stress. The chemicals and signals released by this system have the ability to activate the nerve endings in the skin. 

The release of chemicals such as substance P, histamine, and nerve growth factor can intensify itching¹⁰. This sets up a vicious cycle in which the itching causes tension, which in turn exacerbates the itching. The itchy-scratch cycle is what this is called, and it can occur even if your skin appears to be perfectly fine. It's not always a skin ailment, but rather your neurological system responding to irritation.

The limbic system and the periaqueductal grey are two other brain regions that are impacted by stress and are involved in emotion and sensation. Your body's itching sensation may intensify in certain places. Therefore, when you're already stressed or overloaded, even minor triggers can feel much more annoying.

Summary

NP is a nerve-related disorder that produces burning or itching in the upper back, beneath the shoulder blades. The skin and deep back muscles, like the erector spinae, are affected by irritation of the dorsal rami spinal nerves. These symptoms can be due to the spinal abnormalities or tense muscles. Additionally, stress has a significant impact since it triggers the sympathetic nervous system, which increases itching sensitivity and feeds the vicious cycle of stress and scratching. The secret to reducing symptoms is to control both stress and nerve irritation.