Clinical differentiation between simple obesity and secondary diseases
Differential Diagnosis. 1. Differentiation between simple obesity and Cushing's syndrome. A small number of simple obesity cases may present with similar symptoms to Cushing's syndrome. These may be accompanied by hypertension, impaired glucose tolerance, amenorrhea or oligomenorrhea, acne and/or hirsutism, and atypical purple striae, which are thin and mostly white, with a few being pale red. However, simple obesity generally lacks central obesity, thin skin, plethora, ecchymosis, and typical purple striae. X-ray examination shows no enlargement of the sella turcica, less significant increase in urinary 17-hydroxycorticosteroids, and no significant increase in plasma cortisol.
It also preserves the normal diurnal secretion rhythm. However, in cases of Cushing's syndrome, urinary free cortisol is >552 nanomoles/24 hours; urinary 17-hydroxycorticosteroids are >55.2 micromoles/24 hours; serum cortisol morning baseline values are higher than normal, and the rhythm is lost, i.e., >138 nanomoles/liter at 0:00; in the overnight dexamethasone suppression test, serum cortisol is >110 nanomoles/liter or decreases by <50% at 8:00 AM the following morning; in the low-dose dexamethasone suppression test, on the second day after medication, urinary free cortisol is >55.2 nanomoles/24 hours, and 17-hydroxycorticosteroids are >11 micromoles/24 hours.
2. Differential Diagnosis of Simple Obesity and Cushing's Syndrome. Most patients with Cushing's syndrome present with rapid weight gain, as changes in weight and body shape are easily noticed. However, other manifestations of Cushing's syndrome, such as hypertension, fatigue, hypokalemia, osteoporosis, and amenorrhea, may appear at different stages of the disease or vary in severity and are therefore often overlooked by patients. Since the causes of Cushing's syndrome are mostly pituitary tumors, hypothalamic-pituitary dysfunction, or adrenal cortical tumors, timely differentiation from simple obesity is crucial for patient treatment and prognosis.
The two conditions share some similarities in their clinical presentation: Cushing's syndrome is characterized by central obesity, with patients having relatively thin limbs and fat primarily deposited in the face, neck, shoulders, abdomen, and proximal extremities, resulting in characteristic facial features such as a "buffalo hump," "frog belly," and "moon face." Simple obesity, on the other hand, is usually uniform obesity. 70%–90% of Cushing's syndrome patients experience elevated blood pressure, with mild to moderate hypertension being the most common. This elevated blood pressure is related to increased glucocorticoid levels and enhanced vascular responsiveness to catecholamines.
Some individuals with simple obesity also have hypertension, and their common underlying cause may be hyperinsulinemia and insulin resistance. Cushing's syndrome, due to elevated cortisol levels, enhances glycogenolysis and gluconeogenesis, resulting in impaired glucose tolerance in 60%–90% of cases, and 10% can be diagnosed with steroid-induced diabetes. Simple obesity can also manifest as impaired glucose tolerance due to decreased insulin receptor density and insulin resistance on adipocyte membranes, leading to reduced insulin sensitivity. In Cushing's syndrome patients, the proteolytic effect of cortisol causes thinning of the skin.
Skin elastic fibers are prone to rupture, and cortisol stimulates the proliferation of erythrocytes in the bone marrow, resulting in pleocytic skin. Wide, purplish-red or pale red spindle-shaped striae are easily observed in areas such as the lower abdomen, inner and outer thighs, popliteal fossa, and armpits. A small number of patients with simple obesity may also show scattered white or pale red fine, short streaks on the lower abdomen and thighs, which is related to rapid weight gain. Patients with Cushing's syndrome have significantly elevated plasma cortisol levels, accompanied by circadian rhythm disturbances. Individuals with simple obesity may have mildly elevated plasma cortisol levels, but their diurnal secretion rhythm is normal.
3. Differential Diagnosis of Simple Obesity and Hypothyroidism. Hypothyroidism is a clinical syndrome caused by insufficient synthesis, secretion, or physiological effects of thyroid hormones. Due to varying degrees of thyroid hormone deficiency, different durations of illness, and insidious onset, clinical manifestations differ greatly, often leading to missed or misdiagnosis due to atypical symptoms or lack of experience among non-endocrinologists. Adult hypothyroidism patients often present with edema and weight gain, easily misdiagnosed as simple obesity; therefore, clinical differentiation is necessary.
Both conditions commonly occur in middle-aged women. When middle-aged women gain weight and become overweight, it's natural to think of it as a sign of middle-age "weight gain." If other clinical manifestations of hypothyroidism are not prominent, diagnosis and treatment may be delayed. Simple obesity involves subcutaneous fat accumulation, with normal skin elasticity and luster. Weight gain in hypothyroid patients is mainly due to increased mucopolysaccharide content in the subcutaneous tissue, interstitium, and serous cavity fluid, leading to tissue and serous cavity edema. Due to decreased thyroid hormone levels, hypothyroid patients exhibit symptoms of low metabolism, such as slow heart rate, cold intolerance, rough skin, dryness, and reduced sweating.
Symptoms of hypothyroidism include sluggishness in movement and expression, constipation, and a sallow, dull complexion, especially a prolonged relaxation time of the Achilles tendon reflex. Myxedema in hypothyroidism can manifest as hoarseness, facial edema, muscle pain, pericardial and pleural effusion, cardiomegaly (though heart failure is uncommon), and non-pitting edema of the lower extremities. Due to the deficiency of thyroid hormones, the stimulation of bone marrow hematopoietic function is weakened, erythropoietin levels decrease, and gastric acid deficiency leads to impaired iron and vitamin B₁₂ absorption. Most hypothyroid patients have mild to moderate anemia, with a pale, slightly yellowish complexion, which is significantly different from the rosy complexion of simple obesity.
In patients with hypothyroidism, serum T3, T4, FT3, and FT4 are all decreased. In primary hypothyroidism, where the lesion is in the thyroid gland, serum TSH is elevated. In secondary hypothyroidism, where the lesion is in the hypothalamus-pituitary region, serum TSH is decreased or at the low end of normal. The measurement of thyroid hormones is the gold standard for diagnosing hypothyroidism. Clinically, whenever hypothyroidism is suspected, a timely diagnosis can be made by measuring serum T3, T4, and TSH. These changes are not observed in simple obesity.
4. Differential Diagnosis of Simple Obesity and Polycystic Ovary Syndrome (PCOS). Polycystic ovary syndrome (PCOS) is a common and highly complex pathological condition in women of reproductive age, caused by endocrine and glucose metabolism abnormalities, characterized by excessive androgens and anovulation. Typical clinical manifestations include secondary amenorrhea, hirsutism, obesity, and infertility. 50%–70% of women with PCOS are obese, and this obesity is caused by excessive androgens. Excess androgens primarily cause fat accumulation in the upper body.
Besides thickening of abdominal wall fat, the main cause of obesity is fat accumulation between abdominal viscera, often presenting as abdominal or central obesity. Simple obesity is mostly uniform, with some exhibiting a "pear-shaped" shape. The vast majority of obese individuals also have hyperinsulinemia. The direct cause of elevated plasma insulin levels is insulin resistance, which is determined by genetic factors and its degree correlates with weight gain or loss. Insulin resistance is considered a primary initiating factor for a series of obesity-related diseases, including hypertension and dyslipidemia.
Both simple obesity and PCOS involve insulin resistance and compensatory hyperinsulinemia. As pancreatic β-cell function gradually decompensates, some obese individuals eventually develop type 2 diabetes. Most PCOS patients exhibit hirsutism. Hair distribution tends to be masculinizing, with more hair on the face, around the lips, buttocks, and lower legs, and thicker eyebrows and pubic hair. Some individuals with simple obesity may also experience increased hair growth, but without the masculinizing characteristics. Typical PCOS is not difficult to distinguish from simple obesity, although some cases of PCOS present with atypical clinical manifestations.
It can be diagnosed by measuring sex hormone levels and observing ovarian morphological changes. PCOS is mostly an anovulatory menstrual disorder with signs of excessive androgens, such as masculinization, hirsutism, and acne. The plasma testosterone level of PCOS patients is 3.7–5.21 namool/L, and half of the patients have a mild increase in androstenedione and dehydroepiandrosterone. Gonadotropin secretion is uncoordinated, with luteinizing hormone (LH) being higher than urinary follicle-stimulating hormone (FSH) during the follicular phase, and the LH/FSH ratio increases (>2.5–3). LH remains at a high level, affecting follicular development, so most patients are anovulatory.
Macroscopic examination during laparoscopy revealed that the ovaries were 1/3 to 1/2 larger than normal, with a thickened capsule and multiple follicles of varying sizes visible beneath the capsule; no corpus luteum was observed. Transvaginal ultrasound also showed enlarged ovaries with an increased number of follicles arranged in a necklace-like pattern along the cortex. Magnetic resonance imaging (MRI) revealed typical polycystic ovary syndrome (PCOS) findings.