​Symptoms and Signs – Differential Diagnosis of Impotence
• Endocrine: hyperprolactinemia, diabetes mellitus (DM), Cushing’s syndrome, hypothyroidism or hyperthyroidism, abnormality of hypothalamic-pituitary-testicular axis
• Medications
• Neurogenic: autonomic or sensory neuropathy, spinal cord trauma or tumor, cerebrovascular accident (CVA), multiple sclerosis (MS), temporal lobe epilepsy
• Peyronie’s disease
• Prostatectomy
• Psychogenic
• Systemic illness: renal failure, chronic obstructive pulmonary disease (COPD), cirrhosis of liver, myotonic dystrophy
• Vascular: arterial insufficiency, venous leakage, arteriovenous (AV) malformation, local trauma

​Symptoms and Signs – Differential Diagnosis of Persistent Hyperventilation
• Sepsis
• Salicylate intoxication
• Psychogenic (e.g., anxiety)
• Metabolic acidosis (e.g., diabetes, uremia)
• Hepatic coma
• Fibrotic lung disease
• Fever
• CNS disorders (midbrain and pontine lesions)

​Symptoms and Signs – Differential Diagnosis of  Serum Hyperviscosity 
• Systemic lupus erythematosus (SLE)
• Rheumatoid arthritis (RA)
• Polycythemia
• Monoclonal gammopathies (Waldenström’s macroglobulinemia, multiple myeloma)
• Leukemia
• Hyperfibrinogenemia

​Symptoms and Signs – Differential Diagnosis of  Hypoalbuminemia
• Severe burns
• Rapid IV hydration
• Protein-losing enteropathies (inflammatory bowel disease [IBD])
• Prolonged immobilization
• Pregnancy
• Poor nutritional status
• Nephrotic syndrome
• Neoplasia
• Lymphomas
• Liver disease
• Hypervitaminosis A
• Chronic inflammatory diseases
• Chronic glomerulonephritis

​Symptoms and Signs – Differential Diagnosis of Hypoaldosteronism
Pseudohypoaldosteronism: renal unresponsiveness to aldosterone. In this condition, both renin and aldosterone levels are elevated.Pseudohypoaldosteronism can be caused by medications (spironolactone), chronic interstitial nephritis, systemic disorders (systemic lupus erythematosus, amyloidosis), or primary mineralocorticoid resistance.

​Symptoms and Signs – Differential Diagnosis of Hypocalcemia
• Renal insufficiency: hypocalcemia caused by:
• Increased calcium deposits in bone and soft tissue secondary to increased serum PO4−3 level
• Decreased production of 1,25-dihydroxyvitamin D
• Excessive loss of 25-OHD (nephrotic syndrome)
• Hypoalbuminemia: each decrease in serum albumin (g/L) will decrease serum calcium by 0.8 mg/dL but will not change free (ionized) calcium.
• Vitamin D deficiency
• Malabsorption (most common cause)
• Inadequate intake
• Decreased production of 1,25-dihydroxyvitamin D (vitamin D–
dependent rickets, renal failure)
• Decreased production of 25-OHD (parenchymal liver disease)
• Accelerated 25-OHD catabolism (phenytoin, phenobarbital)
• End-organ resistance to 1,25-dihydroxyvitamin D
• Hypomagnesemia: hypocalcemia caused by
• Decreased parathyroid hormone (PTH) secretion
• Inhibition of PTH effect on bone
• Pancreatitis, hyperphosphatemia, osteoblastic metastases: hypocalcemia is secondary to increased calcium deposits (bone, abdomen).
• Pseudohypoparathyroidism: autosomal recessive disorder characterized by short stature, shortening of metacarpal bones, obesity, and mental retardation; the hypocalcemia is secondary to congenital end-organ resistance to PTH.
• Idiopathic hypoparathyroidism, surgical removal of parathyroids (e.g., neck surgery)
• “Hungry bones syndrome”: rapid transfer of calcium from plasma into bones after removal of a parathyroid tumor
• Sepsis
• Massive blood transfusion (as a result of ethylenediaminetetraacetic acid [EDTA] in blood)

​Symptoms and Signs – Differential Diagnosis of Hypocapnia
• Pulmonary embolism
• Pulmonary disease (asthma, interstitial fibrosis)
• Pregnancy
• Pneumonia, pneumonitis
• Pain
• Metabolic acidosis
• Medications (salicylates, β-adrenergic agonists, progesterone, methylxanthines)
• Hyperventilation
• High altitude
• Hepatic failure
• Fever, sepsis
• Congestive heart failure (CHF)
• CNS lesions

​Symptoms and Signs – Differential Diagnosis of Hypochloremia
• Vomiting
• Thiazide diuretic administration
• Syndrome of inappropriate antidiuretic hormone (SIADH)
• Salt-losing nephritis
• Primary aldosteronism
• Gastric suction
• Diarrhea
• Diaphoresis
• Diabetic ketoacidosis (DKA)
• Continuous infusion of D5W
• Congestive heart failure (CHF)
• Burns
• Addison’s disease

​Symptoms and Signs – Differential Diagnosis of Hypochondriasis
• Underlying medical condition, such as multiple sclerosis, hypothyroidism, or systemic lupus erythematosus (SLE)
• Somatization disorder
• Body dysmorphic disorder (restricted to a circumscribed concern about appearance)
• Factitious disorder or malingering
• Generalized anxiety disorder with health concerns as one worry among many others
• Major depressive disorder with health concerns occurring only during depressive episodes
• Psychosis, such as may occur with depression or schizophrenia

Symptoms and Signs – Differential Diagnosis of Hypogonadism
HYPERGONADOTROPIC HYPOGONADISM
• Hormone resistance (androgen, luteinizing hormone [LH] insensitivity)
• Gonadal defects (e.g., Klinefelter’s syndrome, myotonic dystrophy)
• Drug induced (e.g., spironolactone, cytotoxins)
• Alcoholism, radiation induced
• Mumps orchitis
• Anatomic defects, castration
HYPOGONADOTROPIC HYPOGONADISM
• Pituitary lesions (neoplasms, granulomas, infarction, hemochromatosis, vasculitis)
• Drug induced (e.g., glucocorticoids)
• Hyperprolactinemia
• Genetic disorders (Laurence-Moon-Biedl syndrome, Prader-Willi
syndrome)
• Delayed puberty
• Other: chronic disease, nutritional deficiency, Kallmann’s syndrome, idiopathic isolated LH or follicle-stimulating hormone (FSH) deficiency