Differential Diagnosis for Cold Intolerance, Headache, and Lightheadedness

Primary Endocrine Etiologies

The American College of Endocrinology suggests that hypothyroidism should be the leading diagnosis when cold intolerance presents with headache and lightheadedness 1, 2
Cold intolerance is a cardinal symptom of hypothyroidism, along with fatigue, weight gain, constipation, and depression 1
Headache occurs as a common manifestation of thyroid dysfunction 1
Lightheadedness can result from the cardiovascular effects of low thyroid hormone 1
Morning thyroid function tests, including TSH and free T4, are essential for diagnosis 1
High TSH with low free T4 confirms primary hypothyroidism 1
The Endocrine Society recommends additional thyroid peroxidase (TPO) antibody testing if biochemical hypothyroidism is confirmed 1

The American Heart Association defines orthostatic hypotension as a sustained BP drop ≥20 mmHg systolic or ≥10 mmHg diastolic within 3 minutes of standing 3
Lightheadedness is the predominant feature of orthostatic hypotension, with headache as a secondary symptom 3
The American College of Cardiology states that lightheadedness is a recognized anginal equivalent that must be considered in appropriate clinical contexts, particularly in patients with known coronary disease, diabetes, or >20% 10-year Framingham risk 4

The American Headache Society suggests that migraine requires ≥5 attacks lasting 4-72 hours with specific characteristics, but cold intolerance and persistent lightheadedness make isolated migraine unlikely 5, 6
The International Headache Society defines chronic migraine as headache ≥15 days/month for >3 months, with ≥8 days meeting migraine criteria, but cold intolerance is not part of the diagnostic criteria 8

The American Academy of Neurology recommends always evaluating for dangerous secondary causes before confirming primary headache diagnosis, including thunderclap headache, "worst headache of life", new headache after age 50, progressive worsening headache, headache awakening patient from sleep, focal neurological signs, neck stiffness, and unexplained fever 6, 9

The Endocrine Society recommends urgent thyroid function testing, including morning TSH and free T4, as the first step in diagnosis 1
The American College of Physicians suggests assessing for red flag features, including complete neurological examination, and obtaining neuroimaging if any red flags are present 6, 9
The American Heart Association recommends measuring BP and heart rate supine and after 3 minutes standing to assess for orthostatic hypotension 3