What could be the underlying cause of my cold hands and feet, psoriasis, eczema, meteorism, occasional fatty stool, constipation, and slow progress in strength training, despite normal serum markers for vitamin B12, iron, iodine, and thyroid function, and a history of high globulin antibodies and positive thyreoglobulin antibodies, now negative, as a 32-year-old male, 183cm, 78kg, with a testosterone level of 460ng/dL, FSH 3.4, and normal vitamin D, B12, iron, and ferritin levels?

Evaluation of Subclinical Hypothyroidism and Optimization of Thyroid Function

Your constellation of symptoms—cold extremities, slow muscle development, psoriasis/eczema, and gastrointestinal issues—most likely stems from subclinical hypothyroidism (TSH 3-4 mIU/L in a reference range of 0.4-3.8), which warrants treatment optimization given your symptomatic presentation and history of positive thyroglobulin antibodies.

Primary Issue: Suboptimal Thyroid Function

Your TSH of 3-4 mIU/L exceeds the upper limit of your laboratory's reference range (0.4-3.8 mIU/L), indicating subclinical hypothyroidism 1. While your free T4 and T3 are within range, this does not exclude clinically significant thyroid dysfunction, particularly given:

• Previous autoimmune thyroid disease: You had positive thyroglobulin antibodies (204 IU/mL) 5 years ago, indicating a history of autoimmune thyroiditis despite current negative antibody status 1
• Classic hypothyroid symptoms: Cold intolerance (hands/feet cold at 21°C), difficulty building muscle mass, constipation, and skin manifestations are hallmark features of inadequate thyroid hormone 1
• TSH above optimal range: Even "high-normal" TSH (>2.5-3.0 mIU/L) can cause symptoms in some individuals, particularly those with autoimmune thyroid history 1

Recommended Actions for Thyroid Management

1. Repeat thyroid function testing including TSH, free T4, free T3, and TPO antibodies (thyroid peroxidase antibodies) in the morning around 8 AM for accurate assessment 1
2. Consider trial of levothyroxine therapy if TSH remains elevated above 3.8 mIU/L, targeting TSH between 0.5-2.5 mIU/L, as symptomatic patients with subclinical hypothyroidism often benefit from treatment 1
3. Monitor for autoimmune thyroid disease progression with annual thyroid function testing, as your history of positive thyroglobulin antibodies indicates ongoing risk 1

Critical pitfall: Do not dismiss subclinical hypothyroidism simply because free T4/T3 are "in range"—the TSH is the most sensitive marker, and your value exceeds the reference range 1.

Secondary Considerations

Testosterone and Muscle Development

Your testosterone of 460 ng/dL is in the lower-normal range for a 32-year-old male. While not frankly hypogonadal, this may contribute to slow strength gains and difficulty building muscle mass. However, thyroid dysfunction must be corrected first, as hypothyroidism can suppress testosterone production and TSH levels of 4-10 IU/L can occur due to lack of cortisol's inhibitory effect on pituitary function 1.

Vitamin and Mineral Status

Despite consuming adequate RDA amounts, consider:

• Vitamin B12 monitoring: Autoimmune thyroid disease is associated with autoimmune gastritis and pernicious anemia, which can cause B12 malabsorption despite adequate intake 2, 3. Your current B12 is "in range" but the specific value matters—levels below 200 pg/mL warrant supplementation 3
• Ferritin optimization: Your ferritin increased from 59 to 92 µg/L, which is improved but still suboptimal for men (ideal >100 µg/L for tissue function) 1. Iron deficiency can cause cold extremities and impair exercise performance 1
• Zinc assessment: Given your psoriasis and eczema, measure serum zinc levels, as zinc deficiency is associated with skin conditions and impaired immune function 4

Gastrointestinal Symptoms

Your meteorism, occasional fatty-appearing stool (though easily cleaned with water suggests it may not be true steatorrhea), and constipation pattern suggests:

• Hypothyroid-related gut dysmotility: Constipation is a classic hypothyroid symptom and should improve with thyroid optimization 1
• Not malabsorption: Normal fecal elastase rules out pancreatic insufficiency, negative celiac testing excludes celiac disease, and your description of stool (easily cleaned with water) argues against true fat malabsorption 1
• Consider small intestinal bacterial overgrowth (SIBO): Meteorism with constipation in the context of hypothyroidism (which slows gut motility) raises suspicion for SIBO, which can be evaluated with hydrogen breath testing if symptoms persist after thyroid optimization

Psoriasis and Eczema Management

Your skin conditions require dermatologic management:

• Topical therapy: High-potency topical corticosteroids combined with vitamin D analogues (calcipotriene) are first-line for limited psoriasis 5
• Screen for psoriatic arthritis: Up to 25-30% of psoriasis patients develop joint involvement; assess for joint pain, swelling, or stiffness 5
• Metabolic screening: Psoriasis is associated with metabolic syndrome, cardiovascular disease, and diabetes—ensure screening for hypertension, dyslipidemia, and glucose abnormalities 1

Important caveat: Widespread dermatitis can cause euthyroid sick syndrome (altered thyroid hormone levels despite normal thyroid function), but this is unlikely given your chronic symptoms 6.

Algorithmic Approach to Your Case

1. Immediate priority: Recheck thyroid function (TSH, free T4, free T3, TPO antibodies) and initiate levothyroxine if TSH >3.8 mIU/L, targeting TSH 0.5-2.5 mIU/L 1
2. Concurrent evaluation: Measure serum zinc, confirm specific B12 value (supplement if <200 pg/mL), and optimize ferritin to >100 µg/L 1, 2, 3, 4
3. Reassess in 6-8 weeks: After thyroid optimization, evaluate whether cold extremities, muscle development, and GI symptoms improve
4. If symptoms persist despite thyroid optimization: Consider testosterone replacement (if repeat morning testosterone <300 ng/dL with symptoms), SIBO testing for persistent GI symptoms, and dermatology referral for systemic psoriasis therapy if skin involvement worsens 1, 5

Monitoring Schedule

• Thyroid function: Every 6-8 weeks until TSH stable in target range, then annually 1
• B12 levels: Annually in patients with autoimmune thyroid disease 2, 3
• Metabolic screening: Blood pressure, lipids, glucose annually given psoriasis 1
• Testosterone: Recheck after thyroid optimization if symptoms persist

Final critical point: Your symptom improvement after strength training (lasting up to 1 day) suggests transient increases in metabolic rate and circulation, which supports the hypothesis that baseline metabolic function (thyroid-driven) is suboptimal and requires correction 1.