Morvan’s disease

Morvan's disease, also known as Morvan's chorea or analgesic paralysis with whitlows, is a rare clinical syndrome that is now understood to be a specific manifestation of the underlying neurological disorder syringomyelia. It is characterized by a combination of sensory loss, muscle wasting, and significant tissue changes in the extremities, particularly the hands and forearms.

The condition is named after the French physician Augustin Marie Morvan, who first described this collection of symptoms in 1883 among fishermen and farmers in Brittany, France. He noted the distinctive progressive and painless ulcerations of their fingertips.

Pathophysiology: The Role of Syringomyelia

Morvan's disease is not a separate disease entity but rather a clinical presentation of syringomyelia. Syringomyelia is a chronic disorder involving the spinal cord, in which a fluid-filled cyst, known as a syrinx, forms and expands within the spinal cord's central canal.

This growing syrinx exerts pressure on and eventually destroys the surrounding nerve fibers. Crucially, it often damages the nerve fibers of the spinothalamic tract that cross over in the center of the spinal cord. These fibers are responsible for transmitting pain and temperature sensations to the brain. The damage to these specific fibers, while initially sparing the nerve pathways for touch and proprioception (position sense), leads to the hallmark symptoms of the condition.

The "trophic" tissue changes, such as skin ulceration and changes to nails and bones, are a direct result of this profound sensory loss and associated autonomic nerve dysfunction, which impair the body's ability to regulate, protect, and heal tissues in the affected areas.

Signs and Symptoms

The presentation of Morvan's disease is striking due to the combination of neurological and physical changes. Key features include:

• Profound Sensory Loss: A characteristic loss of pain and temperature sensation in the upper extremities, often in a "cape-like" distribution across the shoulders, arms, and hands. Despite this, the sense of light touch, pressure, and limb position may be preserved. This is known as a dissociated sensory loss.
• Paresthesia: Abnormal sensations such as numbness, tingling, or burning in the forearms and hands often precede or accompany the sensory loss.
• Painless Ulceration and Mutilation: The most distinctive feature is the development of progressive, painless sores, ulcers, and infections on the fingertips. Because of the lack of pain sensation, individuals may suffer repeated burns, cuts, and injuries without realizing it, leading to non-healing wounds, bacterial infections (whitlows), and, in severe cases, resorption of the underlying bone and eventual loss of the fingertips.
• Trophic Changes: Beyond ulceration, other tissue changes include shiny or discolored skin, brittle nails, and excessive sweating (hyperhidrosis) or loss of sweating (anhidrosis).
• Muscle Weakness and Atrophy: As the syrinx expands to affect motor neurons, it causes progressive weakness and wasting of the small muscles of the hands and forearms.

Diagnosis

The diagnosis of Morvan's disease is made based on the unique clinical presentation, which is then confirmed by identifying the underlying syringomyelia. Magnetic Resonance Imaging (MRI) is the definitive diagnostic tool. An MRI of the spine can clearly visualize the syrinx within the spinal cord, confirming the cause of the patient's symptoms.

Treatment and Management

There is no cure for the nerve damage itself; therefore, treatment is aimed at managing the underlying syringomyelia and its symptoms.

• Surgical Intervention: The primary treatment for syringomyelia is often neurosurgery. The goal is to address the root cause of the syrinx formation. This may involve a procedure to decompress a Chiari malformation (a common cause), remove a tumor, or insert a shunt to drain the fluid from the syrinx and reduce pressure on the spinal cord.
• Symptomatic and Supportive Care: This is a crucial aspect of management.
  • Patient Education: Patients must be educated about their lack of pain sensation to meticulously avoid injuries from hot surfaces, sharp objects, and excessive pressure.
  • Wound Care: Regular inspection of the hands and feet for injuries and professional management of any ulcers are essential to prevent infection and severe tissue damage.
  • Physical and Occupational Therapy: These therapies help maintain muscle strength, prevent joint contractures, and adapt daily activities to preserve function and safety.