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Abdominal aortic aneurysm

Absence seizure (petit mal seizure)

Acanthosis nigricans

Achilles tendinitis

Achilles tendon rupture

Acoustic neuroma

Actinic keratosis

Actinic prurigo

Acute angle closure glaucoma

Acute coccidioidomycosis (valley fever)

acute coronary syndrome

Acute intestinal ischemia

Acute kidney failure

Acute liver failure

Acute lymphocytic leukemia

Acute myelogenous leukemia (AML)

Acute porphyrias

Acute respiratory distress syndrome (ARDS)

Acute sinusitis

Addison's disease

Adjustment disorders

Adult ADHD (attention deficit hyperactivity disorder)

Adult intussusception

Adult Still's disease

Age spots (liver spots)

Alcohol intolerance

Alcohol poisoning

Alcoholic hepatitis

Alzheimer's disease

Amyotrophic lateral sclerosis

Angelman syndrome

Ankylosing spondylitis

Anorexia nervosa

Antibiotic associated diarrhea

Antiphospholipid syndrome

Antisocial personality disorder

Aortic dissection

Aortic valve regurgitation

Aortic valve stenosis

Aplastic anemia

Arteriosclerosis

Arteriovenous fistula

Atopic dermatitis (eczema)

Atrial fibrillation

Atrial septal defect (ASD)

Atrioventricular canal defect

Attention deficit hyperactivity disorder (ADHD) in children

Atypical depression

Autoimmune hepatitis

Autonomic neuropathy

Avascular necrosis