What causes the feeling of cold in a patient with potential underlying conditions such as anemia or hypothyroidism?

Why Does She Feel Cold? Pathophysiological Mechanisms

Hypothyroidism as the Primary Cause

If the patient has hypothyroidism, she feels cold because thyroid hormones are essential for maintaining basal metabolic rate and heat production—their deficiency directly reduces thermogenesis and causes cold intolerance as a cardinal symptom. 1

Direct Metabolic Effects

• Thyroid hormones regulate basal metabolic rate, and their deficiency causes decreased heat production at the cellular level, leading to the characteristic cold intolerance seen in hypothyroidism 1
• The reduced metabolic activity results in decreased oxygen consumption and energy expenditure, manifesting clinically as cold skin on physical examination 1
• This is a primary hypothalamic-mediated response where the body's temperature set point and heat generation capacity are fundamentally impaired 1

Cardiovascular Contributions

• Hypothyroidism causes decreased cardiac output and bradycardia, reducing peripheral blood flow and heat distribution to the extremities 1
• The combination of reduced metabolic heat production and impaired circulatory heat distribution creates the subjective sensation of persistent coldness 1

Anemia as a Contributing Mechanism

If anemia coexists with hypothyroidism (occurring in 20-60% of hypothyroid patients), the cold sensation is amplified because reduced oxygen-carrying capacity further impairs cellular metabolism and heat production. 2, 3

Anemia-Hypothyroidism Connection

• Anemia is diagnosed in 20-60% of patients with hypothyroidism and is often the first presenting sign of thyroid dysfunction 2, 3
• Thyroid hormones directly or indirectly stimulate erythroid colony growth through erythropoietin, so their deficiency causes normocytic anemia (the most common type, occurring in 51.6% of cases) 2, 3, 4
• The anemia represents an adaptation to decreased basal metabolism but paradoxically worsens cold intolerance by reducing oxygen delivery to tissues 2, 3

Types of Anemia in Hypothyroidism

• Normocytic anemia (51.6% of cases): Results from thyroid hormone deficiency itself, characterized by reticulopenia, hypoplasia of erythroid lineage, and decreased erythropoietin levels 3, 4
• Microcytic anemia (43.3% of cases): Caused by iron malabsorption and menorrhagia-related iron loss 2, 4
• Macrocytic anemia (up to 55% of cases): Results from vitamin B12 or folate malabsorption; pernicious anemia occurs 20 times more frequently in hypothyroid patients 2, 4

Clinical Significance of Combined Pathology

• The coexistence of iron deficiency anemia and hypothyroidism creates a hyperadrenergic state that can cause intolerance to thyroid hormone replacement 5
• Correction of anemia before or concurrent with thyroid hormone replacement is essential, as the combined metabolic impairment significantly worsens cold intolerance 5

Alternative Vascular Causes

If the cold sensation is localized primarily to the hands and feet rather than generalized, consider Raynaud's phenomenon, which causes episodic vasospasm triggered by cold exposure and affects women four times more often than men. 6

Primary vs Secondary Raynaud's

• Primary Raynaud's disease presents as isolated episodic vasospasm affecting individual digits with characteristic white-blue-red color changes, lasting an average of 23 minutes 6
• Secondary Raynaud's phenomenon involves entire hands with severe, painful episodes that can progress to digital ulcers or gangrene, often associated with connective tissue diseases like systemic sclerosis 6

Critical Distinction

• Digital blood pressure measurement is essential to differentiate arterial occlusion from vasospastic disorders—90 of 91 fingers with cold sensitivity in arterial occlusion show significantly low pressures 6
• Unilateral cold hand suggests arterial occlusion or steal syndrome rather than systemic hypothyroidism and requires urgent vascular evaluation 6

Diagnostic Approach

• Check thyroid-stimulating hormone (TSH) and free thyroxine (T4) levels to confirm hypothyroidism 1
• Obtain complete blood count to identify anemia type and severity 3, 4
• Measure serum iron, vitamin B12, and folate levels if anemia is present 3, 4
• Consider antinuclear antibody (ANA) testing if secondary Raynaud's or connective tissue disease is suspected 6