What could be the underlying cause of a 32-year-old male's cold hands and feet, slow progress in strength training, psoriasis, eczema, and gastrointestinal symptoms, despite normal serum markers for vitamin B12, iron, iodine, and selenium, and a negative celiac blood test, with a history of positive thyreoglobulin antibodies and elevated antistreptolysin quant?

Subclinical Hypothyroidism with Peripheral Vasoconstriction and Dermatological Manifestations

Your TSH of 3-4 (reference 0.4-3.8) indicates subclinical hypothyroidism that is likely contributing to your cold extremities, and this should be treated with levothyroxine titrated to achieve TSH <2.5 mIU/L, particularly given your constellation of symptoms including impaired muscle development and dermatological manifestations. 1

Primary Thyroid Dysfunction Analysis

Your thyroid function tests reveal subclinical hypothyroidism that warrants intervention:

• TSH 3-4 mIU/L is above the upper reference limit of 3.8, indicating inadequate thyroid hormone production despite "normal" free T4 and T3 levels 1
• The British Society of Gastroenterology recommends monitoring thyroid function in patients with autoimmune conditions, and your history of positive thyroglobulin antibodies 5 years ago (204 U/mL, now negative) suggests previous autoimmune thyroiditis that may have caused permanent thyroid damage 1
• Cold extremities at 21°C room temperature are a classic manifestation of hypothyroidism due to decreased metabolic rate and peripheral vasoconstriction 1
• Your slow muscle development and impaired strength training progress align with hypothyroid myopathy, where reduced thyroid hormone impairs protein synthesis and muscle metabolism 1

Dermatological Manifestations Require Dual Consideration

Your psoriasis and eczema presentation suggests two distinct but potentially overlapping processes:

Psoriasis Management in Sensitive Areas

• The American Academy of Dermatology specifies that psoriasis in intertriginous areas (which includes perianal regions causing your "smeary stool" symptoms) presents as erythematous, minimally indurated, well-demarcated plaques with minimal scale 2
• Use low-potency topical corticosteroids only for any genital/perianal psoriatic lesions, as medication penetration is dramatically enhanced by local humidity in these areas 2, 1
• Consider calcineurin inhibitors (tacrolimus or pimecrolimus) for inverse psoriasis, which are highly effective and do not cause skin atrophy 2

Eczema Component

• Your description of eczema alongside psoriasis may represent "eczema in psoriatico," a recognized entity where psoriatic lesions develop spongiotic features, particularly on hands and feet 3
• Apply moderate-potency topical corticosteroid (triamcinolone 0.1% cream) twice daily to eczematous areas, combined with emollients at least once daily using oil-in-water creams or ointments 4

Gastrointestinal Symptoms Warrant IBD Exclusion

Your meteorism, constipation, and perianal symptoms combined with skin manifestations raise concern for inflammatory bowel disease:

• The European Crohn's and Colitis Organisation reports that dermatological complications occur in approximately 22% of IBD patients, with psoriasis and eczema being recognized extra-intestinal manifestations 1, 5
• Research demonstrates that psoriasis patients have significantly higher prevalence of all six cardinal GI symptoms (abdominal pain, bloating, diarrhea, mucus in stool, blood in stool, unintentional weight loss) compared to controls 6
• Your negative celiac serology and normal endoscopy 1 month ago make celiac disease unlikely, but colonoscopy with biopsy is essential to definitively exclude IBD, as upper endoscopy alone is insufficient 5
• The perianal "smeary stool" symptom could represent either psoriatic involvement of the perianal skin or early IBD manifestations 2, 5

Testosterone and Muscle Development

Your testosterone of 460 ng/dL with FSH 3.4 is technically within normal range but suboptimal for a 32-year-old male:

• Subclinical hypothyroidism directly impairs testosterone production and muscle protein synthesis, which explains your poor strength training response 1
• Correcting thyroid function should be the first intervention before considering testosterone supplementation, as thyroid hormone is essential for normal testosterone metabolism 1

Nutritional Status Reassessment

Despite consuming adequate RDA amounts, your absorption may be impaired:

• Vitamin D at 50 ng/mL and B12 at 400 pg/mL are both in the lower half of reference ranges and should be optimized higher (vitamin D >75 ng/mL, B12 >500 pg/mL) given your autoimmune conditions 1
• Your ferritin improvement from 59 to 92 μg/L is positive but still suboptimal for muscle development (target >100 μg/L for males) 1
• Normal fecal elastase makes pancreatic insufficiency unlikely 1

Recommended Diagnostic and Therapeutic Algorithm

Immediate Actions (Next 2 Weeks)

1. Initiate levothyroxine 50-75 mcg daily (based on your 78 kg weight) with goal TSH <2.5 mIU/L, recheck in 6 weeks 1
2. Schedule colonoscopy with biopsy to definitively exclude IBD given your symptom constellation 5
3. Apply low-potency topical corticosteroid to perianal psoriatic areas and moderate-potency corticosteroid to other eczematous areas 2, 4

Short-Term Monitoring (6-12 Weeks)

1. Recheck TSH, free T4, and thyroid antibodies after 6 weeks on levothyroxine 1
2. Increase vitamin D supplementation to achieve levels >75 ng/mL 1
3. Consider B12 supplementation to achieve levels >500 pg/mL despite adequate dietary intake 1

Expected Outcomes

• Cold extremities should improve within 4-8 weeks of achieving optimal thyroid function 1
• Muscle development and strength training response should improve within 8-12 weeks of thyroid optimization 1
• If colonoscopy confirms IBD, systemic therapy (biologics) would address both intestinal and dermatological manifestations simultaneously 1, 5

Critical Pitfalls to Avoid

• Do not dismiss TSH 3-4 as "normal" when it exceeds the upper reference limit and you have classic hypothyroid symptoms 1
• Do not use high-potency topical corticosteroids in the perianal region, as this will cause severe atrophy and worsening symptoms 2
• Do not assume your GI symptoms are purely functional (IBS) without colonoscopy, given the strong association between psoriasis and IBD 5, 6
• Do not continue gluten-free diet without confirmed celiac disease, as this was appropriately negative and unnecessary dietary restriction impairs quality of life 1
• Do not attribute all symptoms to a single cause—your presentation requires addressing thyroid dysfunction, potential IBD, and dermatological conditions as separate but interrelated issues 1, 5