Small fiber neuropathy – a disease with a challenging diagnostic procedure

Small fiber neuropathy – a disease with a challenging diagnostic procedure

Stomachache, leg pain, crying to sleep, headache, incontinence and diarrhea. Jenna Birch’s childhood and most of her adult life was filled with these complications before she was diagnosed with small fiber polyneuropathy – also called small fiber neuropathy.

Jenna Birch, now 28, suffering from pain had made her life so difficult that she wished to escape her own body. She was misdiagnosed as fibromyalgia, irritable bowel syndrome and menstrual disorder and lived with these diagnoses for 18 years, until a doctor finally gave her the correct diagnose: Small fiber polyneuropathy, also called small fiber neuropathy or small fiber peripheral neuropathy. 

Her symptoms started at age of 10 from leg pain, which her parents thought to be “growing pains”, and later developed to headache, stomach ache, incontinence and diarrhea. By age of 16 her symptoms became difficult to hide and thereby kept her down from attending classes to social activities. “Sometimes I wouldn’t eat to avoid digestive issues. Other times I’d cut class, so I didn’t have to sit through six of them in a row, my bladder in agony. I avoided group activities and public outings; I made many excuses” Jenna says. 

 

Small Fiber Neuropathy

Small fiber neuropathy occurs when damage to the peripheral nerves affects the small myelinated fibers (A)  or unmyelinated C fibers. These are sensory nerve fibers that transfer thermal perception and nociception (sensation of pain). These fibers are also involved in a number of autonomic and enteric functions. 
In small fiber polyneuropathy, the condition affects nerve fibers all over the body; the nerve ending damage could be caused by various problems including genetics, autoimmune conditions, injury or diseases. 
Symptoms of small fiber neuropathy can vary widely in severity. In many cases there is a gradual onset of distal symptoms that include vague disturbance of sensation in the feet. Some individuals may also report a cold-like pain, tingling or a pins and needles sensation. Many patients report transient electric shock-like pain, usually lasting only seconds, but quite severe and potentially multiple times per day. In addition to spontaneous pain, many individuals report allodynia (pain to non-painful stimuli) and hyperesthesia (increase in sensitivity of any sense, such as sight, sound, touch and smell). 
Small nerve fiber neuropathy also may result in autonomic and enteric dysfunction. Patients often do not identify the relationship of these symptoms to their sensory complaints; however, when asked, they may report among others diarrhea, constipation, difficulty with urinary frequency, nocturia, and/or voiding. 

 

Diagnosis of Small Fiber 

The history and physical examination findings are the main standards against which all tests are compared, when making a diagnosis of a small fiber neuropathy. A detailed review of the symptoms, rate of progression, and complaints suggestive of autonomic fiber involvement is necessary. However, patients with small fiber neuropathy are expected to have severe pain symptoms with little evidence of neuropathy at clinical examination and nerve conduction study. For this reason, the diagnosis may become difficult and, mainly in patients not afferent to referral centres, occur long time after the onset. However, patients should always be screened for other treatable causes of small fiber neuropathy. Recently, scoring examinations have been developed, and may aid in diagnosis of small fiber neuropathies. In addition, the specific types of pain experienced by patients with small fiber neuropathy may need to be characterized. 

 

Skin Biopsy

Skin biopsy, available for about 20 years, has become a widely accepted technique to investigate the structural integrity of small nerve fibers. This technique can provide a reliable quantification of somatic and autonomic small nerve fibers. A standard 3-mm dermatologic punch biopsy can be taken from any location on the body, but typically is performed on sites of interest in evaluation of a distal small fiber neuropathy (e.g., the lateral distal leg or thigh). By using either bright field immunohistochemistry or indirect immunofluorescence approaches, the number of fibers crossing the dermal/epidermal junction is quantified through standardized means, and results are expressed as the number of intraepidermal nerve fibers per millimeter. 

 

The correct diagnosis

“Those of us with small fiber polyneuropathy look fine. We have learned to mimic “normal”. But inside, the pain is chipping away at us” Jenna says. After several appointments to doctors, hospitals and performing several tests, Jenna got the diagnosis of fibromyalgia in 2011. It is a chronic condition characterized by widespread pain, fatigue, plus sleep and mood issues. She believed in the diagnose for several years, until she spoke to a new doctor, Anne Louise Oaklander, over the phone in 2015. Anne Louise Oaklander, MD, a neurologist and director of the nerve unit at Massachusetts General Hospital, explained to Jenna, that she might be a patient of small fiber neuropathy instead of fibromyalgia. Later, Jenna completed a punch biopsy, which revealed only few nerve endings left in her skin. Finally, in 2015 she received the correct diagnosis to her disease, small fiber polyneuropathy. Jenna expresses her relief this way: “I feel saner and more self-assured now that I have a conclusive diagnosis. I don’t worry that I am making a big deal out of pain, that I am just too weak to handle it”. 
 

Sources

1. The National Center for Biotechnology Information – Diagnosis and Treatment of Pain in Small Fiber Neuropathy: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3086960/
2. Current Option – Small Fiber Neuropathy: https://www.pnsociety.com/files/Resources/2017%20Lauria%20SFN%20review%20C…
3. Health – Before she was diagnosed with Small Fiber Polyneuropathy, Doctors misdiagnosed this woman’s pain for 18 year.: https://www.health.com/condition/pain/small-fiber-neuropathy-misdiagnosed

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