In a patient, muscle cramps on exercise, +ve myoglobulinemia, the disorder is –
**Core Concept**
Muscle cramps on exercise, accompanied by elevated myoglobin levels in the blood, suggest a disorder related to muscle damage or metabolic derangement during physical activity. This condition is often associated with abnormal energy production within muscle cells.
**Why the Correct Answer is Right**
The correct answer is related to McArdle's disease, a genetic disorder caused by a deficiency of myophosphorylase enzyme. This enzyme is crucial for glycogen breakdown and subsequent glucose-1-phosphate production, which is necessary for energy production in muscle cells during high-intensity exercise. When myophosphorylase is deficient, muscle cells cannot generate energy efficiently, leading to exercise-induced muscle cramps, weakness, and rhabdomyolysis, which results in elevated myoglobin levels.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not directly relate to exercise-induced muscle damage or myoglobinemia. Other conditions like hypokalemia or hypocalcemia can cause muscle cramps but do not typically present with elevated myoglobin levels.
**Option B:** This option is incorrect because it refers to a condition that primarily affects the heart, not the skeletal muscles. Hypothyroidism can cause muscle weakness and fatigue but does not typically present with exercise-induced muscle cramps or myoglobinemia.
**Option C:** This option is incorrect because it refers to a condition that primarily affects the nervous system, not the muscles directly. Neuromuscular junction disorders like myasthenia gravis can cause muscle weakness but do not typically present with exercise-induced muscle cramps or myoglobinemia.
**Clinical Pearl / High-Yield Fact**
McArdle's disease is an autosomal recessive disorder, and genetic testing can confirm the diagnosis. Patients with McArdle's disease often have a family history of similar symptoms, and diagnosis can be made based on clinical presentation, muscle biopsy, and enzyme activity assays.
**Correct Answer:** C. McArdle's disease is characterized by exercise-induced muscle cramps, myoglobinemia, and a deficiency of myophosphorylase enzyme.