Differential Diagnosis for a 25-year-old Female with Peripheral Small Fiber Neuropathy

Single Most Likely Diagnosis

• Fibromyalgia or Small Fiber Neuropathy associated with Autoimmune Disorders: Given the presence of peripheral small fiber neuropathy, positive ANA, and low sweat gland density without diabetes, this diagnosis is plausible due to the overlap of symptoms with autoimmune conditions and the specific finding of low sweat gland density which is often seen in small fiber neuropathy.

Other Likely Diagnoses

• Systemic Lupus Erythematosus (SLE): The positive ANA is a hallmark of SLE, and while SLE can cause neuropathy, the presence of small fiber neuropathy and low sweat gland density could be part of the disease's manifestation.
• Sjögren's Syndrome: This autoimmune disorder can cause neuropathy and has been associated with small fiber neuropathy. The low sweat gland density could be related to the exocrine gland dysfunction seen in Sjögren's.
• Rheumatoid Arthritis (RA): Though less commonly associated with small fiber neuropathy directly, RA can have neuropathic manifestations and the positive ANA could be indicative of an underlying autoimmune process.

Do Not Miss Diagnoses

• Amyloidosis: A rare condition that can cause small fiber neuropathy and has a significant impact on mortality and morbidity if not diagnosed and treated early. The low sweat gland density could be a part of systemic amyloid deposition.
• Lyme Disease: Can cause neuropathy and has been associated with small fiber neuropathy. Given its potential for serious complications if untreated, it's crucial not to miss this diagnosis.
• Vitamin Deficiencies (Vitamin B12, Vitamin E): Deficiencies in these vitamins can lead to neuropathy. Although less likely given the other findings, they are critical to rule out due to their potential for reversibility with treatment.

Rare Diagnoses

• Fabry Disease: A genetic disorder leading to small fiber neuropathy due to the accumulation of globotriaosylceramide. It's rare but should be considered, especially given the patient's age and the specific finding of low sweat gland density.
• Tangier Disease: Another rare genetic disorder that affects lipid metabolism and can lead to neuropathy, though it's less commonly associated with small fiber neuropathy specifically.