Scalp pruritus has a variety of sources (Figure 1). Part 1, published in the September 2017 issue of The Dermatologist, discussed inflammatory dermatologic disorders. Part 2 addresses common infectious dermatologic disorders, neuropathic, systemic, and psychogenic disorders (Table).
Tinea capitis is a dermatologic infection caused by dermatophytes.1,2 Although tinea capitis can affect any person, it predominately affects children of African descent.1,2 The main culprit is Trichophyton tonsurans that causes itching and scaling initially, and eventually can evolve to patchy alopecia with black dots or hair-colored dots (due to broken hair shafts).1,2 Gray circular patches with scale, diffuse scale, or diffuse pustules are also possible presentations.2 In severe cases, the infection sites may coalesce into boggy plaques with pustules that are tender called kerions.1 Cervical and suboccipital lymphadenopathy occurs frequently, but is not diagnostic.1,2
Neuropathic causes of pruritus exist in several skin locations such as anogenital, brachioradial, and scalp.13 Scalp dysesthesia was described as a chronic cutaneous disorder without objective findings that predominately affects women.14-16 The disorder exists on a spectrum of only pain, pain and pruritus, or only pruritus. After ruling out localized or systemic organic disease and psychological disease, neuropathic scalp dysesthesia can be diagnosed.14
The pathogenesis is poorly understood, but cervical spine disease (most commonly degenerative disks in C5-C6) leading to chronic muscle tension placed on the occipitofrontalis muscles and scalp aponeurosis may be a factor.15 A single patch of alopecia with pain and/or pruritus with trichoscopy findings of broom hairs, block hairs, and short hairs with trichorrhexis nodosa was considered to be characteristic according to one recent small study.17 In the seminal article, patients with only pruritus did not respond or were less responsive to treatment with low-dose antidepressants.14 Oral or topical gabapentin, and pregabalin may provide relief based on limited evidence.15,16,18
Sensitive scalp is a relatively new disorder on the spectrum of sensitive skin.19,20 Although there is no link to another specific scalp disorder, affected individuals frequently had some scalp disorder or hair loss.19 Greasy or dry scalps may be a predisposing factor, but could also be a consequence of the disorder.19 Pruritus was reported in >35% of patients in 2 studies.19,20 Shampoos were considered to be the main trigger, while temperature extremes, pollution, emotions, dry air, wet air, and water were also possibilities.19,20 Sensitive skin and especially sensitive scalp do not have consensus treatments.21 Avoiding triggers, moisturizers, and anti-inflammatory agents (such as topical calcineurin inhibitors) are potential therapeutic options.21-23
Herpes zoster is a common disorder especially in the elderly population.24,25 Postherpetic pain is a well-recognized sequela of zoster, but postherpetic pruritus can also occur.24 One study indicated that 70.8% of patients with zoster had itch; however, most patients had pain and itch, and only 3.5% reported solely itch.24 The itch percentage declined to 10.5% after 1 year, and was more persistent than postherpetic pain.24 Zoster can present in a variety of skin areas, and the scalp is no exception.24,26-28 The head, face, and neck may have a higher proportion of postherpetic itch compared with extremities or limbs.25,28 Severe case reports of scalp lichenification and self-mutilation due to intractable pruritus have been published.26,27 Data is limited in treatment of postherpetic itch.28,29 An important part of treatment in zoster, and all neuropathic itch, is behavioral modification.28,29 Wearing mittens or hand restraints for nocturnal pruritus might be warrented.28 Local (topical and injectable) anesthetics, and high thoracic epidural catheter with a continuous infusion of bupivacaine and clonidine have shown efficacy.28-31 Tricyclic antidepressants, dual reuptake inhibitors of serotonin and norepinephrine, gabapentin, and pregabalin are also options for neuropathic itch in general.28,31 Doxepin might also be useful due to its tricyclic antidepressant and antihistamine effects; the sedation itself might lower the tendency to itch.28
Neuropathic pruritus has been documented in patients with stroke, brain tumors, or abscesses, nerve entrapment, burns, and much more.27,32 While a scalp specific neuropathic itch in the aforementioned conditions has not been widely established in literature, it is theoretically feasible. Thus, an expanded differential should be in mind for cases of neuropathic scalp itch that do not have a straightforward diagnosis. A referral to a neurologist might also be warranted.33 No clear-cut methods to treat neuropathic itch exist.32 Treatment should be individualized, and the topical and systemic options are similar to treating postherpetic zoster. Other topical treatments include capsaicin and calcineurin inhibitors.27,32
Forty percent of individuals with chronic kidney disease (CKD), with or without dialysis, have pruritus.34,35 The itch is often bilaterally distributed in nondermatomal areas, and can include the head/face.34-36 Although the scalp is not specifically mentioned in the literature, 44% of patients are affected by CKD-associated pruritus have distribution on the head according to one study of 219 patients.37,38 The itch severity can broadly vary, but it can affect quality of life and increase morbidity.34,35 Patients suffering from itch may be more prone to depression, poor sleep, and higher rates of mortality.34,35 Many individuals with CKD may also be affected by xerosis which can worsen itch.34,35 A variety of factors could be in play for the origin of CKD itch such as histamine, uremic toxin, opioids, hyperparathyroidism, and the immune system.34,35 Hypercalcemia and hyperphosphatemia increase the risk of pruritus.34,35
Evidence for treatments for CKD-associated pruritus exist, but clear protocols do not.39 Gabapentin has the best evidence for efficacy.35,39 Central μ-opioid receptors antagonists (naltrexone) and μ-opioid receptor agonists (nalfurafine) demonstrated value in smaller studies.34,35,39 Antihistamines are not effective enough, and have the danger of sedating the elderly population.34,35 Phototherapy, pregabalin, montelukast, cholestyramine, and thalidomide are possible alternative options.35,39 Topical treatments of capsaicin and emollients have shown promise in reducing itch.34,35,39 Treating patients with emollients, which have a low side-effect profile, to reduce xerosis is an important part of lowering the baseline propensity to exacerbate itch in CKD patients.34,35 Utilizing high-permeability dialysis vs conventional dialysis can also improve the pruritus side-effect profile.39
Chronic cholestatic liver disease causes pruritus due to diseases such as primary biliary cirrhosis, chronic hepatitis B and C infection, cholestasis of pregnancy, primary sclerosing cholangitis, and tumors of the pancreatic head.37,40 Although usually the extremities are affected, generalized pruritus does occur.40 Cholestyramine, rifampicin, μ-opioid receptor antagonists, and sertraline are the preferred treatments in that respective order.40-43
Paraneoplastic itch has been observed in both non-Hodgkin lymphoma, Hodgkin lymphoma, and polycythemia vera.44 Severe pruritus can be a presenting symptom of disease, and a marker of disease progression.44,45 Atopic dermatitis presenting for the first time after the age 30 could be a sign of lymphoma, and with enough clinical suspicion may warrant a lymph node exam and an x-ray.45 Data on prevalence and treatment are limited.44,45 Serotonin-norepinephrine reuptake inhibitors, gabapentin, μ-antagonist and κ-agonist opioids, thalidomide, doxepin, and mirtazapine have all been used in small studies and case series.44,45 The best treatment for pruritus is to address the underlying malignancy through multispecialty corroboration.45
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Psychogenic pruritus is a diagnosis of exclusion.46 The French psychodermatology group suggest 3 required main criteria: “localized or generalized pruritus sine materia, chronic pruritus (>6 weeks), and the absence of a somatic cause.”47 Seven additional minor criteria, where at least 3 were needed, from the same group were “a chronological relationship of pruritus with one or several life events that could have psychological repercussions; variations in intensity associated with stress; nocturnal variations; predominance during rest or inaction; associated psychological disorders; pruritus that could be improved by psychotropic drugs; and pruritus that could be improved by psychotherapies.”47 A small study (31 patients) to validate the criteria found that 77% of the patients could be identified.48
Population prevalence of this disorder is not known, but there is female preponderance with an average age of onset around 30 to 45 years.46 Comorbidity with other psychiatric illnesses are common in patients who have chronic itch.46,49 There are no primary skin changes in psychogenic itch, and the distribution of secondary changes (excoriations, erosions, lichenification) are generally in areas where the patient can reach such as extensor surfaces of the extremities, the face, and the scalp.46,50 Insight into the psychogenic nature of the pruritus can vary, but patients cannot stop itching regardless of the degree of comprehension.46 Treatment is generally through antidepressants such as serotonin-norepinephrine reuptake inhibitors, selective serotonin reuptake inhibitors, doxepin, and psychotherapy.46,50
Delusions of parasitosis, or Morgellons disease, is a disorder where patients falsely believe they are infested with parasites or foreign substances in the skin.50 The prevalence is 83.23 per million people in the outpatient setting.50 Patients believe the parasites are crawling in their skin with biting and stinging.50 Many may bring specimens of hair, dead skin, or insects as proof of their disease.50 Excoriations, erosions, ulcers, prurigo nodules, and lichenification are all possible due to attempts to extract the parasites.50
The diagnosis is made clinically after excluding other diseases of neurologic etiology or substance abuse.50 The initial step in treatment is to build trust with the patients.50,51 Using the term Morgellons disease instead of delusions of parasitosis can help build rapport.51 Then, a low-dose antipsychotic medication such as pimozide or risperidone can be used.50,52 Second-generation antipsychotics may be preferred due to a better side-effect profile.50,52
Dermatologists must garner a patient’s perspective of the disease to listen and acknowledge their suffering.52 While the belief is false, the morbidity is not.52 Some patients may also be willing to talk to a psychiatrist or a psychologist, and a referral should be provided if possible.52
Scalp pruritus is a complex topic with a vast variety of causative disorders. This article is not meant to be an exhaustive list for the genesis and treatment of scalp itch. Furthermore, the literature for the epidemiology, clinical manifestations, and treatment of scalp pruritus is limited. However, the pertinence of recognizing and addressing this common disorder in the dermatology setting is paramount. If we do not, we may be left scratching our own heads.
Dr McMichael, The Mane Point Section Editor, is professor and chair in the department of dermatology at Wake Forest Baptist Health in Winston-Salem, NC.
Disclosure: Dr McMichael has received grants from Allergan and Proctor & Gamble. She is a consultant for Allergan, eResearch Technology, Inc, Galderma, Guthey Renker, Johnson & Johnson, Keranetics, Merck & Co, Inc, Merz Pharmaceuticals, Proctor & Gamble, Samumed, and Incyte. She receives royalties from Informa Healthcare and UpToDate and also has conducted research for Samumed.
Mr Subash reports no relevant financial relationships.
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