Introduction

Have you ever felt pain with burning, stabbing, or aching sensations that are without obvious cause? 

Central Pain Syndrome (CPS) or more specifically central neuropathic pain (CNP) is a challenging medical condition resulting in ongoing pain from damage or dysfunction to the central nervous system (CNS). This pain does not come from external cuts nor bruises, but from the part of CNS that processes sensory and pain signals, causing complex and debilitating pain that often follows a wide range of neurological disorders or trauma.

While the varying, devastating pain can make ordinary daily activities challenging. Recognising their manifestations and diagnostic criteria can raise awareness and empower individuals affected by CPS and their families to get timely medical care and better management for the condition. 

This article will explain the key features and diagnostic criteria of CPS in simple terms, to promote the symptom identification and understand the doctors’ diagnosis among the general public.  

Understanding central pain syndrome 

What is CPS? 

Central pain syndrome (CPS) or central neuropathic pain (CNP) is a neurological disorder resulting from injury or malfunction within the central nervous system (CNS), including the brain, brainstem, and spinal cord. Instead of pain that arises from external stimuli or tissue damage to the peripheral nerves, muscles, joints, or skin, like a cut or a bruise. CPS is the disruption or damage to the thalamus which causes overly excited or altered communication along the pain-processing sensory pathways. As a result, the CNS becomes too sensitive in amplifying, misinterpreting signals and generating pain, even in absence of an obvious trigger. 

Common causes of CPS 

CPS can be caused by a wide variety of neurological conditions or any events that disrupt or damage the CNS like stroke, spinal cord injuries (SCIs), multiple sclerosis (MS), brain /spinal cord tumors and traumas. While its onset can be immediate or after weeks to months upon initial injury, the varying manifestations and extent of pain across the varieties of potential causes can potentially complicate and delay diagnosis. 

The pain in CPS is not simply a symptom, but a result of maladaptive neuroplasticity. It is also commonly seen to be exacerbated by touch, movement, emotional stress, or temperature changes, particularly cold.^1,2 

Key clinical features 

Clinical features are the signs and symptoms that are helpful for doctors to recognize and identify from other pain conditions. 

Common types of pain in CPS 

• Burning sensations: The most common and noticeable symptom of CPS is constant or intermittent feelings of intense heat or feeling like the skin is burning 
• Tingling or pins-and-needles: A persistent and widespread prickling, crawling, or buzzing sensation 
• Electric-shock-like pain: A sudden, sharp jolt of pain that mimics an electrical surge, coming and going without warning, potentially triggered by touch, movement, or emotions
• Aching, stabbing or tearing pain: Deep muscle soreness, sharp jabs, or a sensation being torn from within that usually occurs spontaneously and may worsen with movement, stress, or temperature changes^3,4

Distribution of pain

Pain distribution in CPS is often widespread yet can still vary greatly: pain can be either intermittent or constant, ranging from moderate to severe. CPS Pain can affect one side of the body, for example it could affect your left or right side, or only the lower half of the body. It can also be localised, affecting specific areas like a hand, one side of the face, or a single limb, depending on the CNS area of damage.⁵ 

Other sensory symptoms

In order to protect the body from more damage, pain signals have become a high sensation priority. When it becomes chronic, the nervous system experiences more pain signals for longer periods of time, which increases our sensitivity to both pain and non-pain signals. This will trigger sensory symptoms like:

• Allodynia: Pain from things that shouldn’t hurt normally, like a light touch or clothing brush against the skin, caused by disrupted processing of non-pain signals   
• Hyperalgesia: Heightened pain sensitivity that makes minor discomfort feels severe
• Numbness: A dull, deadened sensation, losing normal touch, like a limb or limbs has fallen asleep⁴ 

Associated symptoms

There are also a wide range of associated symptoms alongside the pain in CPS. Muscle weakness or stiffness may be seen in areas affected by the original CNS injury. Constant pain and poor sleep could often lead to fatigue, where the emotional toll of chronic discomfort can cause anxiety and depression. 

With varied pain patterns, CPS can cause some to experience continuous burning or stabbing sensations, while others face intermittent episodes. The various symptomatic intensifying triggers like stress, cold temperature, movement or touch have also made it highly personalised and unpredictable.

Key diagnostic criteria 

Diagnosing CPS (or central neuropathic pain CNP) can be exceptionally challenging, as pain is subjective. Currently, there is no single or specific set of tests in confirming the CPS/CNP diagnosis, thus physicians must heavily rely on its highly variable presentation and medical history.  Doctors, particularly neurologists and pain specialists, will require a consistent set of standards to rule out other causes of pain and confirm a CPS diagnosis. 

History of CNS damage 

A doctor may interview a patient to learn about the onset, location, and nature of pain. Clear history of an event or condition affecting the brain, brainstem, or spinal cord should be confirmed. These can be a stroke (especially in the thalamus or other pain-processing areas), spinal cord injury (SCI) from trauma, surgery, or compression, as well as other neurological conditions like multiple sclerosis (MS), or brain/spinal cord tumours associated with pain or sensory symptoms that appear weeks to months or longer after the CNS events. 

Characteristics of pain

The pain of CPS typically lasts for months or longer. They are often described as feelings of burning, tingling, or an electric shock. People may experience sensory changes like allodynia, hyperalgesia, or numbness in the affecting area. The location of pain should also be aligned to the damaged or malfunctioning area of the CNS (e.g., one side of the body after a stroke). 

Absence of peripheral causes

The pain in CPS should neither be better explained by other medical conditions, nor should there be evidence of injury or inflammation upon muscles, joints, or peripheral nerves that explains the pain. Medical tests should also be done to rule out these muscles, joints, or peripheral injuries or conditions like arthritis, peripheral nerve damage, fibromyalgia or rheumatoid arthritis. 

Supporting features of diagnosis

The pain of CPS is usually incapable of being simply relieved by typical pain relievers like nonsteroidal anti-inflammatory drugs (NSAIDs) (e.g., ibuprofen or acetaminophen), or stronger opioid medications. Antiseizure medications, several antidepressants, like SNRIs or TCAs, or topical anesthetics are usually prescribed for symptom relief.  

Furthermore, the pain is also prominently shown to worsen with specific triggers like cold weather, stress, or light touch. Reflexes or sensations are also found to be abnormal upon neurological exam findings.⁶ 

Differentiating CPS from other pain conditions

CPS and CNP can be tricky to distinguish amongst other chronic pain conditions due to overlapping symptoms. Their key differences can yet help in differentiating the two conditions from others: 

• Peripheral neuropathies results from damage to peripheral nerves (outside the brain and spinal cord) whereas CPS originates from CNS injury or dysfunction, presenting with both burning pain and sensory abnormalities despite normal nerve conduction studies
• Complex regional pain syndrome (CRPS) often involves features like swelling, colour changes, or trophic skin changes – features that are not typically seen in CPS
• While musculoskeletal pain is often caused by mechanical injury and is localised, pain in CPS is more persistent and widespread, often without clear triggers, varying from person to person
• In contrast to psychogenic pain, in which stress or emotional factors may influence severity or cause exacerbation, CPS has a clear neurological basis rather than psychological
• Fibromyalgia, though widespread, is also distinctive by its association with sleep, memory, and mood issues, which are generally absent in CPS

Diagnostic tests 

In CPS, physical and neurological exams tests for muscle strength, reflexes, and sensory changes may be normal. 

A detailed neurological history, as well as neuroimaging and neurophysiological techniques like MRI, PET, even functional MRI scans, or electroencephalography (EEG) and magnetoencephalography (MEG), will facilitate the detection of underlying CNS lesions or malfunctions. 

Blood tests for inflammation, nerve condition studies, and electromyography (EMG) for peripheral nerves or muscular issues could further provide critical diagnostic clues for accurate diagnosis.⁴ 

Diagnostic challenges 

Owing to the high presentation variability, lack of specific tests, and the often weeks or months of delayed onset after initial CNS injury, a CPS diagnosis is often tricky to confirm and heavily relies on the clinical judgement of experienced neurologists and pain specialists.

Subjectivity to commonly overlapping burning, pins-and-needles, or shooting pain, as well as the unusuality, lack of awareness and knowledge to CPS, can further make individuals struggle to clearly describe their pain that suggests a central origin, causing underrecognition, and even frequent misdiagnosis amongst healthcare providers. 

Summary 

Central Pain Syndrome (CPS) is a chronic pain condition caused by damage or dysfunction to the central nervous system, which often occurs weeks or months after stroke, spinal cord injury, or neurological diseases. With its highly variable key features (such as feelings of burning, tingling or electric-shock like pain, and sensory abnormalities and numbness), it is important to rule out other conditions that may be confused with CPS in order to ensure a correct diagnosis. 

A clear guide on typical clinical features and diagnostic criteria of CPS can enhance neurologists’ and pain specialists’ familiarity and expertise on CPS.  Promoting multidisciplinary cooperation is important for identifying CPS early and tailoring treatment plans, which may focus on pain management and preventing emotional distress, to improve quality of life for the affected individuals.