How is Anagen Effluvium Unique?

An anagen effluvium is extensive hair loss caused by sudden profound disturbances to the matrix cells of the hair follicles. Rather than shedding, the hair is lost by fracturing of the hair shafts at the level of the scalp. The two most common causes of anagen effluvium occur from cancer chemotherapy and from radiation therapy. There are other causes of anagen hair loss, e.g. trichotillomania (compulsive hair pulling), poisoning from toxic plants, loose anagen syndrome, certain disease states (e.g. pemphigus, discoid lupus erythematosus, etc.), heavy metal intoxication, etc. However, this type of anagen hair loss is immediate rather than delayed and the entire hair shaft including the root sheaths is shed. For purposes of simplicity, this article will confine itself to classical anagen effluvium.

Hair growth occurs in no other phase of the hair growth cycle except in the anagen phase. The hair shaft is generated by rapid mitotic cell divisions in the hair matrix to produce hair fiber at a rate of 1 to 1.5cm (approximately ½ inch) per month on the scalp. An anagen effluvium occurs if there is sufficient injury to the rapidly dividing keratinocytes in the hair matrix. The insult damages the keratinocytes and diminishes the metabolic activity of the growing hair shaft. The stoppage of cell division results in a thin, weakened hair shaft that is susceptible to fracture with minimal trauma when it reaches the surface of the scalp. Hair breakage in an anagen effluvium occurs within days to weeks (typically 1 to 3 weeks) following the insult to the follicle. A close examination of the hair will show that the scalp end of the hair shaft is dystrophic with a rapidly tapering configuration (bayonet hair).


Anagen Effluvium and Telogen Effluvium

There are multiple differences between an anagen effluvium and a telogen effluvium. In an anagen effluvium, hair loss occurs because the hair shafts are broken rather than shed. In contrast, the ends of the hairs that are shed in a telogen effluvium have a characteristic club shape with unpigmented proximal ends. The hair loss in an anagen effluvium occurs within days or weeks of the injury to the follicle. Hair loss in a telogen effluvium typically occurs 3 to 4 months after the systemic insult. An anagen effluvium can involve up to 90% of the hair on the head, whereas a telogen effluvium rarely involves more than 50% of the hair on the head. Since ~90% of the hair on the scalp is in the growing phase, an anagen effluvium has the potential to cause almost complete alopecia. The ~10% of the hair follicles in the telogen phase are spared from the toxic insult that results in an anagen effluvium because follicles in telogen are mitotically inactive. You can read more about Telogen Effluvium in our other two articles on the topic here: Telogen Effluvium: Why When and How? | A look at Telogen Effluvium

Differentiating an anagen from a telogen effluvium is usually straightforward and the diagnosis of an anagen effluvium can often be made based solely on the medical history. Nevertheless, there are cases in which the exact diagnosis may be difficult because both entities involve copious amounts of hair loss in a short period of time. And, in fact, an anagen effluvium may occur simultaneously with a telogen effluvium.

Anagen Effluvium - Part 2 Topics: What drugs can Cause Anagen Effluvium? | How it is Treated