All are true about subacute combined degeneration of spinal cord except :
**Core Concept**
Subacute combined degeneration (SCD) of the spinal cord is a progressive neurological disorder caused by a deficiency of vitamin B12 (cobalamin), leading to damage of the spinal cord and peripheral nerves. This condition typically affects the posterior and lateral columns of the spinal cord, resulting in a combination of sensory, motor, and autonomic symptoms.
**Why the Correct Answer is Right**
The underlying mechanism of SCD involves the impaired synthesis of myelin, the fatty substance surrounding nerve fibers, due to a deficiency of methylcobalamin, a coenzyme required for the metabolism of fatty acids and the maintenance of myelin. This leads to demyelination and axonal damage in the spinal cord, particularly affecting the posterior columns (dorsal columns) responsible for transmitting sensory information, and the lateral columns (corticospinal tracts) involved in motor function. The deficiency also affects the synthesis of tetrahydrofolate, essential for DNA synthesis and repair, contributing to the development of megaloblastic anemia.
**Why Each Wrong Option is Incorrect**
* **Option A:** This statement may be true about subacute combined degeneration of the spinal cord, as it is a classic symptom of the condition.
* **Option B:** This statement may be true as well, as the condition typically presents with a combination of sensory and motor symptoms, including weakness, ataxia, and loss of proprioception.
* **Option C:** This statement is incorrect because subacute combined degeneration of the spinal cord is primarily caused by a deficiency of vitamin B12, not vitamin B6 (pyridoxine).
**Clinical Pearl / High-Yield Fact**
It's essential to remember that the diagnosis of subacute combined degeneration of the spinal cord is often delayed due to nonspecific symptoms and the gradual progression of the disease. A high index of suspicion, particularly in patients with megaloblastic anemia or a history of gastric surgery or vegetarian diet, can lead to timely diagnosis and treatment.
**Correct Answer:** C.