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Evaluation and Management of Fatigue in a Young Adult Patient

Screen for hypothyroidism, sleep disorders, acute infections, and mood disorders as these represent the most common and treatable causes of fatigue in young adults, with thyroid dysfunction and depression being particularly important to exclude. 1

Initial Diagnostic Workup

Essential laboratory testing should include:

• TSH measurement to screen thyroid function; if elevated, follow with free T4 and free T3 to differentiate subclinical from overt hypothyroidism 1
• Complete blood count with differential 2
• Iron studies (ferritin, serum iron, TIBC) 2
• Basic metabolic panel 2
• Fasting glucose 2

Thyroid dysfunction must be actively excluded because it is a readily treatable medical cause that commonly presents with fatigue 1. Even when other symptoms are absent, thyroid screening is specifically recommended for patients presenting with fatigue 1.

Sleep Assessment

Document the following sleep parameters systematically:

• Bedtime and wake time 1
• Sleep latency (time to fall asleep) 1
• Number of nocturnal awakenings 1
• Total sleep time 1
• Daytime dysfunction 1

Sleep disturbances affect 30-50% of patients with fatigue and represent one of the most common contributors 1. Insomnia is diagnosed when difficulty falling asleep or maintaining sleep occurs at least three times per week for four weeks or more, accompanied by distress 1. Patients with chronic insomnia report fatigue (low energy, physical tiredness, weariness) more often than actual sleepiness 1.

Screen specifically for:

• Obstructive sleep apnea 1, 2
• Restless legs syndrome 1
• Excessive daytime somnolence 1

Sleep disorders affect 30-75% of fatigued patients, and treating these disorders leads to improvements in fatigue, mood, and overall quality of life 1, 2.

Mood Disorder Screening

Use validated screening instruments:

• PHQ-9 for depression 1
• GAD-7 for anxiety 1

Depression is present in 18.5-33% of fatigued patients and represents the most robust association with persistent fatigue 2. Distress, depression, and anxiety should be routinely assessed in all patients presenting with fatigue 1. Irritability, loss of interest, mild depressive symptoms, and anxiety are common among individuals with chronic fatigue 1.

Younger patients with prior psychiatric history or low socioeconomic status require more thorough probing during assessment 1. Although depression is rarely the primary driver of fatigue, it can exacerbate symptoms, and appropriate treatment may improve overall functioning 1.

Infectious Causes

Acute infectious processes are well-established causes of fatigue and must be considered in the differential diagnosis 1. When fatigue is accompanied by unintentional weight loss or respiratory complaints, perform a more extensive workup to screen for infectious etiologies 1. The presence of acute illness should prompt evaluation for treatable infectious causes before attributing fatigue to chronic conditions 1.

Treatment Algorithm Based on Findings

If hypothyroidism is identified:

• Initiate thyroid hormone replacement therapy 1

If iron deficiency is present (ferritin <50-70 ng/mL):

• Prescribe iron repletion therapy even if CBC is normal 2

If depression or anxiety is diagnosed:

• Consider second-generation antidepressants (SSRIs such as fluoxetine) as first-line pharmacotherapy 3
• Assess patient status, therapeutic response, and adverse effects within 1-2 weeks of initiation 3
• Monitor closely for suicidal ideation, particularly in the first 1-2 months of treatment 3
• Continue therapy for 4-9 months after satisfactory response for first episode 3
• Consider cognitive behavioral therapy 2

If sleep disorder is identified:

• Optimize sleep hygiene: dark, quiet, comfortable sleep environment; regular sleep schedule; avoidance of caffeine and alcohol before bed 2
• Treat specific sleep disorders (OSA, insomnia, restless legs) as indicated 1

For all patients:

• Provide patient education explaining fatigue as a common but treatable symptom 2
• Prescribe physical activity starting with low-intensity exercise and gradually increasing 2
• Reassess fatigue levels at 4-6 weeks after initiating interventions 2
• Rescreen for fatigue at 3-6 month intervals 2

Critical Pitfalls to Avoid

• Do not attribute fatigue to a single cause without first excluding other common contributors, as these conditions frequently coexist 1
• Do not miss hypothyroidism by failing to order thyroid function tests, especially in young women presenting with fatigue 1
• Do not overlook sleep disorders, which are highly prevalent, often underdiagnosed, and readily treatable 1
• Do not miss low ferritin as a readily treatable cause of fatigue, even when CBC is normal 2
• Avoid adding sedating medications that compound fatigue 2