Scalp Neuropathy Associated with Androgenetic Alopecia: JAAD Study

Androgenetic alopecia (AGA) is a common type of alopecia seen predominantly in males. It is a dermatological disorder due to sensitivity to dihydrotestosterone. Another possible contributing factor to AGA is the attachment of the arrector pili muscle (APM), the innervation of which may maintain follicular integrity. Inability to contract the APM might provoke hair loss. Therefore, the authors hypothesized that scalp neuropathy may play a role in AGA and recently published a study on this in the Journal of American Academy of Dermatology.

Study Overview

Scalp sensation in patients of AGA was evaluated on the midfrontal, left, and right frontotemporal recesses, vertex, and occipital regions of 62 men: 30 with Norwood-Hamilton 1 to 2 and 32 with Norwood-Hamilton 3 (clinically significant, AGA group). All participants were healthy with no hair transplants/scars, conditions affecting neural function, or inflammatory scalp conditions. None of the patients were using 5α-reductase inhibitors, minoxidil, or medications/treatments known to affect sensation.

Testing Methods

• Temperature discrimination testing consisted of exposure to glass vials containing either warm (48°C-52°C) or cold (13°C-17°C) water.
• Pressure sensitivity was tested by Semmes-Weinstein filaments of 0.07, 0.4, 2, and 4 g.
• Two-point discrimination testing was done by applying discs with fixed 2- to 25-mm 2-point intervals.

The optimal criterions (by receiver operator characteristic analysis) for pressure threshold and 3-point threshold were determined to be 0.4 g and 20 mm respectively.

Results

Fisher's exact test was used to evaluate the association of AGA with scalp neuropathy. The data were analyzed for men older than 35 years to minimize confounding from age. Forty-two men were included; median age of the AGA group (n=27) was 69 (interquartile range [IQR], 16) and the non-AGA group (n=15) was 60 years (IQR, 15).

• Neuropathy at the vertex of the scalp (>0.4 g sensitivity) was significantly associated with AGA (P=0.025). Forty-eight percent of men with AGA displayed neuropathy at the vertex compared with 13% of men without AGA.
• Neuropathy at the scalp vertex (>20 mm 2-point discrimination distance) was significantly associated with AGA (P=0.002). Sixty-three percent of men with AGA displayed vertex neuropathy compared with 13% of men without AGA.
• Temporal neuropathy (>20 mm 2-point discrimination distance) was also associated with AGA. Sixty-three percent of men with AGA displayed neuropathy at the right frontotemporal recess compared with 20% of men without AGA (P=0.008). Fifty-nine percent of men with AGA displayed neuropathy at the left frontotemporal recess compared with 20% of men without AGA (P=0.015).

No significant association was found between AGA and temperature discrimination. No differences were detected on the midfrontal or occipital scalp.

Conclusion

This is the first study to find an association between scalp neuropathy and AGA. Scalp neuropathy might manifest as autonomic neuropathy and peripheral neuropathy, as the autonomic nervous system controls the APM. The autonomic neuropathy hypothesis is consistent with the fact that disruption of the autonomic nervous system in leprosy triggers localized alopecia. This study shows association rather than cause and effect.

To conclude, this study shows that scalp neuropathy could be associated with androgenetic alopecia but not in a cause and effect manner. Studies in a larger cohort are required to provide robust evidence to support the findings of this study.

Source

Cavanagh G, Goren A, Wambier CG. Scalp neuropathy in androgenetic alopecia. J Am Acad Dermatol. 2022 Jan;86(1):183-184. doi: 10.1016/j.jaad.2021.01.034. Epub 2021 Jan 19. PMID: 33476730.