Sjögren’s syndrome is a systemic autoimmune disorder primarily recognized for its effects on the body’s moisture-producing glands, leading to chronic dryness of the eyes and mouth. It is a disease where the immune system mistakenly attacks healthy tissues. Peripheral neuropathy is damage to the peripheral nerves, which are the communication lines located outside the brain and spinal cord. These nerves transmit sensory information, control muscle movement, and regulate involuntary bodily functions.
A strong association exists between Sjögren’s syndrome and peripheral neuropathy. Neurological complications are common, often affecting 10% to 20% of patients with the syndrome. In some instances, nerve damage can emerge before or concurrently with the classic symptoms of dryness, making neuropathy the initial presentation of Sjögren’s. This neurological involvement demonstrates the syndrome’s ability to affect the entire body.
The Autoimmune Mechanism of Nerve Damage
Nerve damage in Sjögren’s syndrome stems from systemic inflammation caused by the immune system. This process goes beyond the glands, involving immune cells that target the delicate structures of the peripheral nervous system. The immune mechanism can be categorized into two primary forms of attack on the nerves.
One mechanism involves the direct targeting of the nerve cell bodies located in the dorsal root ganglia (DRG), a condition known as sensory neuronopathy. Activated T-lymphocytes, specifically CD4+ T cells, infiltrate the ganglia, causing inflammation and destruction of the sensory neurons. This damage to the cell body is often severe and can result in widespread, debilitating sensory loss.
A second mechanism involves damage to the blood supply of the nerves, known as vasculitis. The small blood vessels (epineurial vessels) that nourish the nerves can become inflamed, restricting blood flow and causing nerve ischemia. This lack of oxygen and nutrients primarily damages the protective myelin sheath that insulates the nerve fibers, or it can directly injure the nerve axon, leading to axonopathy. This process interferes with the nerve fibers’ ability to transmit signals accurately.
Different Types of Neuropathy Associated with Sjögren’s
The neurological complications of Sjögren’s syndrome are highly varied, affecting different sizes and types of nerve fibers, which leads to diverse clinical outcomes. The most frequently identified form is Small Fiber Neuropathy (SFN), which affects the small myelinated A-delta and unmyelinated C fibers that transmit pain and temperature sensations. SFN is characterized by intense neuropathic pain, often described as burning or electric-shock-like sensations.
Another common pattern is Large Fiber Neuropathy, which involves the larger, heavily myelinated nerve fibers responsible for motor function and proprioception. Damage to these larger fibers can manifest as sensorimotor polyneuropathy, causing muscle weakness, reduced deep tendon reflexes, and a loss of vibration sense or balance. While SFN is generally more prevalent, some patients experience a mixed pattern where SFN progresses to include large fiber involvement over time.
Autonomic Neuropathy is a third classification where the immune system targets the involuntary nervous system, which controls functions like heart rate, blood pressure, digestion, and sweating. This type of neuropathy can result in symptoms such as dizziness upon standing (orthostatic intolerance), abnormal sweating, or gastrointestinal motility issues.
Sensory Neuronopathy
Some patients experience Sensory Neuronopathy, a severe form where inflammation is centered on the sensory nerve cell bodies in the dorsal root ganglia. This specific attack leads to a widespread loss of sensation and coordination. This loss is often non-length-dependent, meaning it does not follow the typical pattern of starting in the feet and hands.
Recognizing the Physical Manifestations
The physical manifestations of Sjögren’s-related neuropathy vary significantly, depending on the specific nerve fibers that have been damaged. When small nerve fibers are involved, the primary complaint is chronic pain that can feel like burning, stinging, or electric shocks. Patients may also experience allodynia, which is pain from a stimulus that should not normally be painful, such as the light touch of clothing or a bedsheet.
The loss of sensation is another common manifestation, typically presenting as numbness or a persistent “pins and needles” tingling sensation. This loss of feeling often begins in the feet and hands, a pattern known as length-dependent polyneuropathy. If the larger motor nerve fibers are affected, patients may notice muscle weakness, muscle cramping, or clumsiness in their movements.
In cases of autonomic neuropathy, the symptoms relate to the body’s involuntary control systems. A person might experience lightheadedness or dizziness when moving from a sitting to a standing position due to poor blood pressure regulation. Other manifestations can include problems with digestion, such as feeling full quickly or experiencing constipation, and changes in sweating patterns.
Confirming the Diagnosis
The process of confirming a diagnosis of neuropathy in a patient with Sjögren’s syndrome begins with a comprehensive clinical evaluation and neurological examination. The physician assesses reflexes, muscle strength, and the ability to perceive vibration, temperature, and light touch. Blood tests are also performed to confirm Sjögren’s syndrome itself, primarily by checking for specific autoantibodies like anti-SSA and anti-SSB.
To determine the type and extent of nerve damage, specialized neurophysiological tests are often utilized. Nerve Conduction Studies (NCS) and Electromyography (EMG) measure the electrical activity of the larger motor and sensory nerves and muscles. Abnormalities in these tests indicate large fiber or sensorimotor neuropathy.
However, these electrical tests are often normal in cases of Small Fiber Neuropathy (SFN). A skin biopsy is performed to confirm SFN, involving a small sample of skin, usually from the leg, to count the density of the intraepidermal nerve fibers. A reduced density of these nerve endings provides objective evidence of small fiber damage, a common finding in Sjögren’s syndrome patients experiencing chronic neuropathic pain.