Differential Diagnosis for a 59-year-old Male with Marked Fatigue for One Month

Single Most Likely Diagnosis

• Anemia: Given the nonspecific nature of fatigue, anemia is a common and often overlooked cause, especially in older adults. It can result from various factors such as chronic blood loss, nutritional deficiencies, or chronic diseases.

Other Likely Diagnoses

• Diabetes Mellitus: Type 2 diabetes is prevalent in this age group and can cause fatigue due to high blood sugar levels affecting energy production and possibly leading to complications like neuropathy.
• Hypothyroidism: A condition where the thyroid gland doesn't produce enough thyroid hormone, leading to fatigue, among other symptoms. It's more common in older adults and can be subtle in its presentation.
• Chronic Kidney Disease (CKD): CKD can lead to fatigue due to the buildup of toxins, anemia, and electrolyte imbalances. It's often asymptomatic in its early stages but can be detected through routine blood and urine tests.
• Depression: A common condition in older adults that can manifest with fatigue, among other symptoms like changes in mood, appetite, and sleep patterns.

Do Not Miss Diagnoses

• Acute Leukemia: Although rare, acute leukemia can present with fatigue due to anemia, thrombocytopenia, or the disease process itself. It requires prompt diagnosis and treatment.
• Lymphoma: Both Hodgkin and non-Hodgkin lymphoma can cause fatigue, along with other symptoms like weight loss, night sweats, and lymphadenopathy.
• Chronic Obstructive Pulmonary Disease (COPD): Severe COPD can lead to fatigue due to poor oxygenation and increased work of breathing.
• Heart Failure: Fatigue is a common symptom of heart failure, resulting from decreased cardiac output and possible anemia or electrolyte imbalances.

Rare Diagnoses

• Addison's Disease: A rare endocrine disorder where the adrenal glands do not produce enough cortisol and aldosterone, leading to fatigue, among other symptoms like weight loss and changes in skin pigmentation.
• Pernicious Anemia: A rare cause of vitamin B12 deficiency due to the lack of intrinsic factor, leading to fatigue, neurological symptoms, and gastrointestinal issues.
• Myasthenia Gravis: An autoimmune disease affecting the neuromuscular junction, causing muscle weakness and fatigue that worsens with activity and improves with rest.
• Sleep Apnea: Although not rare, it's often underdiagnosed and can cause significant fatigue due to disrupted sleep patterns.