McArdle Disease (Glycogen Storage Disease Type V): This condition is characterized by the deficiency of myophosphorylase enzyme, leading to an inability to break down glycogen to glucose for energy in muscles. It presents with elevated CK levels due to muscle damage during exercise and elevated lactic acid as the body shifts to anaerobic metabolism. The asymptomatic presentation at rest is typical, with symptoms often appearing during or after physical activity.

Mitochondrial Myopathies: These are a group of disorders affecting the mitochondria, the energy-producing structures within cells. They can lead to elevated lactic acid levels due to impaired aerobic metabolism and elevated CK from muscle damage. Symptoms can be variable and may include muscle weakness, but some individuals may be asymptomatic or have mild symptoms.
Carnitine Palmitoyltransferase (CPT) Deficiency: This is a metabolic disorder affecting the breakdown of fatty acids for energy. It can cause elevated CK levels due to muscle damage, especially after prolonged exercise or fasting, and may lead to elevated lactic acid levels as the body relies more on anaerobic metabolism.

Pompe Disease (Glycogen Storage Disease Type II): Although less common, this lysosomal storage disorder leads to glycogen accumulation in muscles, causing damage. It can present with elevated CK and lactic acid levels. Early diagnosis is crucial as enzyme replacement therapy is available.
Very Long-Chain Acyl-CoA Dehydrogenase (VLCAD) Deficiency: This is a fatty acid oxidation disorder that can cause severe episodes of illness, especially during fasting or infections. It may present with elevated CK and lactic acid levels and is critical to diagnose due to the risk of life-threatening episodes.

Kearns-Sayre Syndrome (KSS): A mitochondrial myopathy characterized by progressive external ophthalmoplegia, pigmentary retinopathy, and cardiac conduction defects, typically presenting before the age of 20. Elevated lactic acid and CK levels can be seen, but the syndrome's distinct clinical features usually guide the diagnosis.
MELAS Syndrome (Mitochondrial Encephalomyopathy, Lactic Acidosis, and Stroke-like episodes): This mitochondrial disorder can present with a variety of symptoms including seizures, stroke-like episodes, and lactic acidosis. While it's rare, the presence of neurological symptoms alongside elevated lactic acid and CK levels would prompt consideration of this diagnosis.